diff --git a/cura/BuildVolume.py b/cura/BuildVolume.py
index 7c965c6cdf..70578d0e02 100755
--- a/cura/BuildVolume.py
+++ b/cura/BuildVolume.py
@@ -442,7 +442,7 @@ class BuildVolume(SceneNode):
 
     def _updateExtraZClearance(self) -> None:
         extra_z = 0.0
-        extruders = ExtruderManager.getInstance().getMachineExtruders(self._global_container_stack.getId())
+        extruders = ExtruderManager.getInstance().getUsedExtruderStacks()
         use_extruders = False
         for extruder in extruders:
             if extruder.getProperty("retraction_hop_enabled", "value"):
diff --git a/cura/Settings/ContainerManager.py b/cura/Settings/ContainerManager.py
index 0d776aec20..9707ca4909 100644
--- a/cura/Settings/ContainerManager.py
+++ b/cura/Settings/ContainerManager.py
@@ -333,11 +333,25 @@ class ContainerManager(QObject):
     @pyqtSlot(str, result = bool)
     def isContainerUsed(self, container_id):
         Logger.log("d", "Checking if container %s is currently used", container_id)
-        containers = self._container_registry.findContainerStacks()
-        for stack in containers:
-            if container_id in [child.getId() for child in stack.getContainers()]:
-                Logger.log("d", "The container is in use by %s", stack.getId())
-                return True
+        # check if this is a material container. If so, check if any material with the same GUID is being used by any
+        # stacks.
+        container_ids_to_check = [container_id]
+        container_results = self._container_registry.findInstanceContainers(id = container_id, type = "material")
+        if container_results:
+            this_container = container_results[0]
+            container_guid = this_container.getMetaDataEntry("GUID")
+            # check all material container IDs with the same GUID
+            material_containers = self._container_registry.findInstanceContainers(GUID = container_guid,
+                                                                                  type = "material")
+            if material_containers:
+                container_ids_to_check = [container.getId() for container in material_containers]
+
+        all_stacks = self._container_registry.findContainerStacks()
+        for stack in all_stacks:
+            for used_container_id in container_ids_to_check:
+                if used_container_id in [child.getId() for child in stack.getContainers()]:
+                    Logger.log("d", "The container is in use by %s", stack.getId())
+                    return True
         return False
 
     @pyqtSlot(str, result = str)
diff --git a/cura/Settings/MachineManager.py b/cura/Settings/MachineManager.py
index 7fb9c3b0a2..e946c18790 100755
--- a/cura/Settings/MachineManager.py
+++ b/cura/Settings/MachineManager.py
@@ -916,6 +916,8 @@ class MachineManager(QObject):
             global_quality = quality_manager.findQualityByQualityType(quality_type, global_machine_definition, [], global_quality = True)
         else:
             global_quality = quality_manager.findQualityByQualityType(quality_type, global_machine_definition, [material])
+        if not global_quality:
+            global_quality = self._empty_quality_container
 
         # Find the values for each extruder.
         extruder_stacks = ExtruderManager.getInstance().getActiveExtruderStacks()
@@ -929,6 +931,8 @@ class MachineManager(QObject):
                 quality_changes = quality_changes_list[0]
             else:
                 quality_changes = global_quality_changes
+            if not quality_changes:
+                quality_changes = self._empty_quality_changes_container
 
             material = stack.material
             quality = quality_manager.findQualityByQualityType(quality_type, global_machine_definition, [material])
diff --git a/resources/definitions/fdmprinter.def.json b/resources/definitions/fdmprinter.def.json
index a259fa4226..650b125153 100755
--- a/resources/definitions/fdmprinter.def.json
+++ b/resources/definitions/fdmprinter.def.json
@@ -997,7 +997,7 @@
                     "type": "[int]",
                     "default_value": "[ ]",
                     "value": "skin_angles",
-                    "enabled": "roofing_pattern != 'concentric'",
+                    "enabled": "roofing_pattern != 'concentric' and roofing_layer_count > 0 and top_layers > 0",
                     "limit_to_extruder": "roofing_extruder_nr",
                     "settable_per_mesh": true
                 },