prevent reloading reference annotations on loading .ifc #4478

1) if reference annotation was changed, it would reload discarding the changes
2) even if reference annotation wasn't changed it would still reload them producing noise in .ifc changes

src/blenderbim/blenderbim/core/drawing.py

@@ -388,11 +388,11 @@ def sync_references(ifc, collector, drawing_tool, drawing=None):
         should_delete_existing_annotation = False
         should_create_annotation = False
 
+        # remove annotation only if the reference object was changed
+        # otherwise we rely on the existing annotation
         if annotation:
             if reference_obj and (ifc.is_moved(reference_obj) or ifc.is_edited(reference_obj)):
                 should_delete_existing_annotation = True
-            elif not reference_obj:
-                should_delete_existing_annotation = True
 
         if (should_delete_existing_annotation or not annotation):
             should_create_annotation = True