diff --git a/src/caosdb/apiutils.py b/src/caosdb/apiutils.py
index 9090109feb6c4d554fa0c7eaf297375775980cfb..9d2f3c4cc343305eaff986031dfe3adc8f45dbc2 100644
--- a/src/caosdb/apiutils.py
+++ b/src/caosdb/apiutils.py
@@ -297,6 +297,7 @@ def compare_entities(old_entity: Entity, new_entity: Entity, compare_referenced_
                     # list of references
                     elif isinstance(prop.value, list) and isinstance(matching[0].value, list):
                         # all elements in both lists actually are entity objects
+                        # TODO: check, whether mixed cases can be allowed or should lead to an error
                         if all([isinstance(x, Entity) for x in prop.value]) and all([isinstance(x, Entity) for x in matching[0].value]):
                             # can't be the same if the lengths are different
                             if len(prop.value) == len(matching[0].value):