Set field handle overrides on CustomFieldBehavior on layout save

Fixes #14166
Fixes #14221
Resolves #14233

CHANGELOG.md

@@ -37,6 +37,7 @@
 - Fixed a bug where all checkboxes would appear checked within selected Matrix blocks. 
 - Fixed a bug where Recent Entries widgets were getting mangled when new entries were created via Quick Post widgets.
 - Fixed a bug where linked chip labels weren’t getting focus rings.
+- Fixed an error that could occur when field handles were overridden. ([#14166](https://github.com/craftcms/cms/issues/14166), [#14221](https://github.com/craftcms/cms/issues/14221))
 
 ## 5.0.0-alpha.8 - 2024-01-23
 

src/services/Fields.php

@@ -1047,6 +1047,13 @@ public function saveLayout(FieldLayout $layout, bool $runValidation = true): boo
         // Refresh CustomFieldBehavior in case any custom field handles were just added/removed
         $this->updateFieldVersion();
 
+        // Tell the current CustomFieldBehavior class about the fields, since they might have custom handles
+        foreach ($layout->getCustomFieldElements() as $layoutElement) {
+            if (isset($layoutElement->handle)) {
+                CustomFieldBehavior::$fieldHandles[$layoutElement->handle] = true;
+            }
+        }
+
         return true;
     }