diff --git a/Editor/API/ObjectRegistry.cs b/Editor/API/ObjectRegistry.cs
index 5337f08..d8eb307 100644
--- a/Editor/API/ObjectRegistry.cs
+++ b/Editor/API/ObjectRegistry.cs
@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text;
 using System.Threading;
 using nadena.dev.ndmf.runtime;
 using UnityEngine;
@@ -117,6 +118,22 @@ public ObjectRegistry(Transform avatarRoot, ObjectRegistry parent = null)
             _parent = parent;
         }
 
+        internal string RegistryDump()
+        {
+            var sb = new StringBuilder();
+
+            foreach (var group in _obj2ref.GroupBy(kvp => kvp.Value))
+            {
+                var source = group.Key.Object == null ? "<null>" : group.Key.Object.name;
+                var instances = group.Select(kvp => kvp.Key.GetInstanceID() + " [" + kvp.Key.name + "]").ToArray();
+
+                sb.Append("\tGroup source ").Append(source).Append(": ").Append(string.Join(", ", instances))
+                    .Append("\n");
+            }
+
+            return sb.ToString();
+        }
+
         /// <summary>
         ///     Returns the ObjectReference for the given object, using the ambient ObjectRegistry.
         /// </summary>
@@ -135,6 +152,17 @@ ObjectReference IObjectRegistry.GetReference(UnityObject obj, bool create)
 
             if (objref != null || !create)
             {
+#if NDMF_TRACE_OBJREG
+                if (objref != null)
+                {
+                    Debug.Log("[ObjectRegistry] Returning reference for " + obj.GetInstanceID() + " [" + obj.name +
+                              "]: " + objref.GetHashCode());
+                }
+                else
+                {
+                    Debug.Log("[ObjectRegistry] No reference for " + obj.GetInstanceID() + " [" + obj.name + "]");
+                }
+#endif
                 return objref;
             }
 
@@ -148,6 +176,9 @@ ObjectReference IObjectRegistry.GetReference(UnityObject obj, bool create)
             objref = new ObjectReference(obj, path);
             _obj2ref[obj] = objref;
 
+#if NDMF_TRACE_OBJREG
+            Debug.Log("[ObjectRegistry] Created reference for " + obj.GetInstanceID() + " [" + obj.name + "]: " + objref.GetHashCode());
+#endif
             return objref;
         }
 
@@ -193,6 +224,14 @@ ObjectReference IObjectRegistry.RegisterReplacedObject(ObjectReference oldObject
                 throw new ArgumentException(
                     "RegisterReplacedObject must be called before GetReference is called on the new object");
 
+            var oldObj = "<" + oldObject.GetHashCode() + ">";
+            if (oldObject.Object != null)
+                oldObj = oldObject.Object.GetInstanceID() + " [" + oldObject.Object.name + "]";
+
+#if NDMF_TRACE_OBJREG
+            Debug.Log("[ObjectRegistry] Registering replacement for " + oldObj + " -> " + newObject.GetInstanceID() + " [" + newObject.name + "]");
+#endif
+            
             _obj2ref[newObject] = oldObject;
 
             return oldObject;
diff --git a/Editor/PreviewSystem/ComputeContext.cs b/Editor/PreviewSystem/ComputeContext.cs
index 760c7fd..cc99f03 100644
--- a/Editor/PreviewSystem/ComputeContext.cs
+++ b/Editor/PreviewSystem/ComputeContext.cs
@@ -4,6 +4,7 @@
 using System.Threading.Tasks;
 using JetBrains.Annotations;
 using nadena.dev.ndmf.cs;
+using UnityEngine;
 
 #endregion
 
@@ -28,7 +29,7 @@ static ComputeContext()
         ~ComputeContext()
         {
             if (!IsInvalidated)
-                UnityEngine.Debug.LogError("ComputeContext " + Description + " was GCed without being invalidated!");
+                Debug.LogError("ComputeContext " + Description + " was GCed without being invalidated!");
         }
         
         #endif
diff --git a/Editor/PreviewSystem/IRenderFilter.cs b/Editor/PreviewSystem/IRenderFilter.cs
index edd0a62..daffd1a 100644
--- a/Editor/PreviewSystem/IRenderFilter.cs
+++ b/Editor/PreviewSystem/IRenderFilter.cs
@@ -7,7 +7,6 @@
 using System.Linq;
 using System.Threading.Tasks;
 using JetBrains.Annotations;
-using NUnit.Framework;
 using UnityEngine;
 
 #endregion
@@ -82,6 +81,11 @@ public override int GetHashCode()
 
             return hashCode;
         }
+
+        public string ToString()
+        {
+            return "RenderGroup(" + string.Join(", ", Renderers.Select(r => r.name)) + ")";
+        }
     }
 
     internal sealed class RenderGroup<T> : RenderGroup
diff --git a/Editor/PreviewSystem/Rendering/NodeController.cs b/Editor/PreviewSystem/Rendering/NodeController.cs
index 7d860f7..b8438a4 100644
--- a/Editor/PreviewSystem/Rendering/NodeController.cs
+++ b/Editor/PreviewSystem/Rendering/NodeController.cs
@@ -85,37 +85,64 @@ internal void OnFrame()
         public static Task<NodeController> Create(
             IRenderFilter filter,
             RenderGroup group,
-            List<(Renderer, ProxyObjectController, ObjectRegistry)> proxies)
+            List<(Renderer, ProxyObjectController, ObjectRegistry)> proxies,
+            string trace
+        )
         {
-            return Create(filter, group, ObjectRegistry.Merge(null, proxies.Select(p => p.Item3)), proxies);
+            return Create(filter, group, ObjectRegistry.Merge(null, proxies.Select(p => p.Item3)), proxies, trace);
         }
 
         public static async Task<NodeController> Create(
             IRenderFilter filter,
             RenderGroup group,
             ObjectRegistry registry,
-            List<(Renderer, ProxyObjectController, ObjectRegistry)> proxies
+            List<(Renderer, ProxyObjectController, ObjectRegistry)> proxies,
+            string trace
         )
         {
             var context =
-                new ComputeContext("NodeController for " + filter + " on " + group.Renderers[0].gameObject.name);
-
+                new ComputeContext("NodeController " + trace + " for " + filter + " on " +
+                                   group.Renderers[0].gameObject.name);
+#if NDMF_TRACE_FILTERS
+            UnityEngine.Debug.Log("[NodeController Create] " + trace + " Filter=" + filter + " Group=" +
+                      group.Renderers[0].gameObject.name +
+                      " Registry dump:\n" + registry.RegistryDump());
+#endif
             IRenderFilterNode node;
             using (var scope = new ObjectRegistryScope(registry))
             {
+                var savedMaterials = group.Renderers.Select(r => r.sharedMaterials).ToArray();
+                
                 node = await filter.Instantiate(
                     group,
                     proxies.Select(p => (p.Item1, p.Item2.Renderer)),
                     context
                 );
+
+                for (var i = 0; i < group.Renderers.Count; i++)
+                {
+                    if (group.Renderers[i].sharedMaterials.SequenceEqual(savedMaterials[i])) continue;
+
+                    Debug.LogWarning("[NodeController Create] Renderer " + group.Renderers[i].gameObject.name +
+                                     " sharedMaterials changed during instantiation of " + filter + " in " +
+                                     " group " + group + ". Restoring original materials.");
+                    group.Renderers[i].sharedMaterials = savedMaterials[i];
+                }
             }
 
+#if NDMF_TRACE_FILTERS
+            Debug.Log("[NodeController Post-Create] " + trace + " Filter=" + filter + " Group=" +
+                      group.Renderers[0].gameObject.name +
+                      " Registry dump:\n" + registry.RegistryDump());
+#endif
+            
             return new NodeController(filter, group, node, proxies, new RefCount(), context, registry);
         }
 
         public async Task<NodeController> Refresh(
             List<(Renderer, ProxyObjectController, ObjectRegistry)> proxies,
-            RenderAspects changes
+            RenderAspects changes,
+            string trace
         )
         {
             var registry = ObjectRegistry.Merge(null, proxies.Select(p => p.Item3)
@@ -151,7 +178,7 @@ RenderAspects changes
             }
             else if (node == null)
             {
-                return await Create(_filter, _group, registry, proxies);
+                return await Create(_filter, _group, registry, proxies, trace);
             }
             else
             {
diff --git a/Editor/PreviewSystem/Rendering/ProxyPipeline.cs b/Editor/PreviewSystem/Rendering/ProxyPipeline.cs
index 289fe37..6e6ffee 100644
--- a/Editor/PreviewSystem/Rendering/ProxyPipeline.cs
+++ b/Editor/PreviewSystem/Rendering/ProxyPipeline.cs
@@ -112,7 +112,7 @@ private async Task Build(ProxyObjectCache proxyCache, IEnumerable<IRenderFilter>
             _ctx = context; // prevent GC
 
 #if NDMF_DEBUG
-            System.Diagnostics.Debug.WriteLine($"Building pipeline {_generation}");
+            Debug.WriteLine($"Building pipeline {_generation}");
 #endif
 
             var filterList = filters.ToImmutableList();
@@ -120,6 +120,15 @@ private async Task Build(ProxyObjectCache proxyCache, IEnumerable<IRenderFilter>
 
             var activeStages = _targetSet.ResolveActiveStages(context);
 
+#if NDMF_TRACE_FILTERS
+            var sb = new System.Text.StringBuilder();
+            foreach (var stage in activeStages)
+            {
+                sb.Append("\t").Append(stage.Filter).Append(" on ").Append(stage.Groups).Append("\n");
+            }
+            UnityEngine.Debug.Log($"[ProxyPipeline] Active stages for pipeline {_generation}:\n{sb}");
+#endif
+
             Dictionary<Renderer, Task<NodeController>> nodeTasks = new();
             int total_nodes = 0;
             int reused = 0;
@@ -148,6 +157,9 @@ private async Task Build(ProxyObjectCache proxyCache, IEnumerable<IRenderFilter>
                     total_nodes++;
                     
                     groupIndex++;
+
+                    var trace = $"Gen{_generation}/Stage{i}/Group{groupIndex}";
+                    
                     var resolved = group.Renderers.Select(r =>
                     {
                         if (nodeTasks.TryGetValue(r, out var task))
@@ -192,7 +204,8 @@ private async Task Build(ProxyObjectCache proxyCache, IEnumerable<IRenderFilter>
                             var proxies = items.Result.ToList();
 
 #if NDMF_DEBUG
-                            System.Diagnostics.Debug.WriteLine($"Creating node for {stage.Filter} on {group.Renderers[0].gameObject.name} for generation {_generation}");
+                            Debug.WriteLine(
+                                $"Creating node for {stage.Filter} on {group.Renderers[0].gameObject.name} for generation {_generation}");
 #endif
                             
                             if (priorNode != null)
@@ -200,7 +213,7 @@ private async Task Build(ProxyObjectCache proxyCache, IEnumerable<IRenderFilter>
                                 RenderAspects changeFlags = proxies.Select(p => p.Item2.ChangeFlags)
                                     .Aggregate((a, b) => a | b);
 
-                                var node = await priorNode.Result.Refresh(proxies, changeFlags);
+                                var node = await priorNode.Result.Refresh(proxies, changeFlags, trace);
                                 if (node != null)
                                 {
                                     reused++;
@@ -209,8 +222,8 @@ private async Task Build(ProxyObjectCache proxyCache, IEnumerable<IRenderFilter>
 
                                 refresh_failed++;
                             }
-                            
-                            return await NodeController.Create(stage.Filter, group, items.Result.ToList());
+
+                            return await NodeController.Create(stage.Filter, group, items.Result.ToList(), trace);
                         })
                         .Unwrap();
 
@@ -235,7 +248,7 @@ await Task.WhenAll(_stages.SelectMany(s => s.NodeTasks))
             //Debug.WriteLine($"Total nodes: {total_nodes}, reused: {reused}, refresh failed: {refresh_failed}");
 
 #if NDMF_DEBUG
-            System.Diagnostics.Debug.WriteLine($"Pipeline {_generation} is ready");
+            Debug.WriteLine($"Pipeline {_generation} is ready");
 #endif
 
             foreach (var stage in _stages)
diff --git a/UnitTests~/NodeControllerTest.cs b/UnitTests~/NodeControllerTest.cs
index dc71164..77b286e 100644
--- a/UnitTests~/NodeControllerTest.cs
+++ b/UnitTests~/NodeControllerTest.cs
@@ -98,7 +98,8 @@ public void TestObjectRegistryProcessing()
                 {
                     (r1, poc1, or1),
                     (r2, poc2, or2)
-                }
+                },
+                ""
             ).Result;
 
             IObjectRegistry reg2 = nodeController.ObjectRegistry;