diff --git a/cookbook/helper/open_data_importer.py b/cookbook/helper/open_data_importer.py
index c032f37c..e598d3fd 100644
--- a/cookbook/helper/open_data_importer.py
+++ b/cookbook/helper/open_data_importer.py
@@ -209,6 +209,8 @@ class OpenDataImporter:
             if obj['open_data_slug'] in existing_data or obj['name'] in existing_data_names:
                 # rather rare edge cases object A has the slug and object B has the name which would lead to uniqueness errors
                 if obj['open_data_slug'] in existing_data and obj['name'] in existing_data_names and existing_data[obj['open_data_slug']]['pk'] != existing_data_names[obj['name']]['pk']:
+                    # TODO this fails if objects are parent/children of a tree
+                    # TODO this does not merge nicely (with data), write better merge method (or use generalized one if available when reading this)
                     source_obj = Food.objects.get(pk=existing_data[obj['open_data_slug']]['pk'])
                     del existing_data[obj['open_data_slug']]
                     source_obj.merge_into(Food.objects.get(pk=existing_data_names[obj['name']]['pk']))
diff --git a/cookbook/views/api.py b/cookbook/views/api.py
index eb2523f8..1173d747 100644
--- a/cookbook/views/api.py
+++ b/cookbook/views/api.py
@@ -262,7 +262,9 @@ class MergeMixin(ViewSetMixin):
 
             try:
                 if isinstance(source, Food):
-                    source.properties.remove()
+                    source.properties.all().delete()
+                    source.properties.clear()
+                    UnitConversion.objects.filter(food=source).delete()
 
                 for link in [field for field in source._meta.get_fields() if issubclass(type(field), ForeignObjectRel)]:
                     linkManager = getattr(source, link.get_accessor_name())