diff --git a/qubesusbproxy/core3ext.py b/qubesusbproxy/core3ext.py
index f74bf93..dd02505 100644
--- a/qubesusbproxy/core3ext.py
+++ b/qubesusbproxy/core3ext.py
@@ -421,47 +421,66 @@ def on_qdb_change(self, vm, event, path):
         current_devices = dict((dev.ident, dev.frontend_domain)
             for dev in self.on_device_list_usb(vm, None))
 
+        # send events about devices detached/attached outside by themselves
+        # (like device pulled out or manual qubes.USB qrexec call)
         # compare cached devices and current devices, collect:
-        # - newly appeared devices
-        # - devices disconnected from a vm
-        # - devices connected to a vm
-        new_devices = set()
-        connected_devices = dict()
-        disconnected_devices = dict()
-        devices_cache_for_vm = self.devices_cache[vm.name]
-        for dev_id, connected_to in current_devices.items():
-            if dev_id not in devices_cache_for_vm:
-                new_devices.add(dev_id)
-                device = USBDevice(vm, dev_id)
-                vm.fire_event('device-added:usb', device=device)
-            elif devices_cache_for_vm[dev_id] != current_devices[dev_id]:
-                if devices_cache_for_vm[dev_id] is not None:
-                    disconnected_devices[dev_id] = devices_cache_for_vm[dev_id]
-                if current_devices[dev_id] is not None:
-                    connected_devices[dev_id] = current_devices[dev_id]
-        for dev_id, connected_to in devices_cache_for_vm.items():
+        # - newly appeared devices (ident)
+        # - devices attached from a vm to frontend vm (ident: frontend_vm)
+        # - devices detached from frontend vm (ident: frontend_vm)
+        # - disappeared devices, e.g. plugged out (ident)
+        added = set()
+        attached = dict()
+        detached = dict()
+        removed = set()
+        cache = self.devices_cache[vm.name]
+        for dev_id, front_vm in current_devices.items():
+            if dev_id not in cache:
+                added.add(dev_id)
+                if front_vm is not None:
+                    attached[dev_id] = front_vm
+            elif cache[dev_id] != front_vm:
+                cached_front = cache[dev_id]
+                if front_vm is None:
+                    detached[dev_id] = cached_front
+                elif cached_front is None:
+                    attached[dev_id] = front_vm
+                else:
+                    # front changed from one to another, so we signal it as:
+                    # detach from first one and attach to the second one.
+                    detached[dev_id] = cached_front
+                    attached[dev_id] = front_vm
+
+        for dev_id, cached_front in cache.items():
             if dev_id not in current_devices:
-                device = USBDevice(vm, dev_id)
-                vm.fire_event('device-removed:usb', device=device)
+                removed.add(dev_id)
+                if cached_front is not None:
+                    detached[dev_id] = cached_front
+
+        for dev_id, front_vm in detached.items():
+            dev = USBDevice(vm, dev_id)
+            asyncio.ensure_future(front_vm.fire_event_async(
+                'device-detach:usb', device=dev))
+        for dev_id in removed:
+            device = USBDevice(vm, dev_id)
+            vm.fire_event('device-removed:usb', device=device)
+        for dev_id in added:
+            device = USBDevice(vm, dev_id)
+            vm.fire_event('device-added:usb', device=device)
+        for dev_ident, front_vm in attached.items():
+            dev = USBDevice(vm, dev_ident)
+            asyncio.ensure_future(front_vm.fire_event_async(
+                'device-attach:usb', device=dev, options={}))
 
         self.devices_cache[vm.name] = current_devices
-        # send events about devices detached/attached outside by themselves
-        # (like device pulled out or manual qubes.USB qrexec call)
-        for dev_ident, front_vm in disconnected_devices.items():
-            dev_id = USBDevice(vm, dev_ident)
-            asyncio.ensure_future(front_vm.fire_event_async('device-detach:usb',
-                                                            device=dev_id))
-        for dev_ident, front_vm in connected_devices.items():
-            dev_id = USBDevice(vm, dev_ident)
-            asyncio.ensure_future(front_vm.fire_event_async('device-attach:usb',
-                                                            device=dev_id,
-                                                            options={}))
+
         for front_vm in vm.app.domains:
             if not front_vm.is_running():
                 continue
             for assignment in front_vm.devices['usb'].get_assigned_devices():
-                if assignment.backend_domain == vm and \
-                        assignment.ident in new_devices:
+                if (assignment.backend_domain == vm
+                        and assignment.ident in added
+                        and assignment.ident not in attached
+                ):
                     asyncio.ensure_future(self._attach_and_notify(
                         front_vm, assignment.device, assignment.options))
 
@@ -610,8 +629,8 @@ async def on_device_detach_usb(self, vm, event, device):
     async def on_domain_start(self, vm, _event, **_kwargs):
         # pylint: disable=unused-argument
         for assignment in vm.devices['usb'].get_assigned_devices():
-            device = assignment.device
-            await self.on_device_attach_usb(vm, '', device, options={})
+            asyncio.ensure_future(self._attach_and_notify(
+                vm, assignment.device, assignment.options))
 
     @qubes.ext.handler('domain-shutdown')
     async def on_domain_shutdown(self, vm, _event, **_kwargs):