diff --git a/SAS/TMSS/backend/test/t_scheduling_units.py b/SAS/TMSS/backend/test/t_scheduling_units.py
index b5d7eb0e6cc925c535cd607deefd6a10878b7439..2bee1ef9aa57c5b26339c948844ea29edff97e63 100644
--- a/SAS/TMSS/backend/test/t_scheduling_units.py
+++ b/SAS/TMSS/backend/test/t_scheduling_units.py
@@ -503,32 +503,31 @@ class SchedulingUnitBlueprintIndirectModificationsTestCase(unittest.TestCase):
 
 
             # ---------------------------------------------------------------
-            # use the specifications_doc from the draft for some 'user'-edits
+            # try to use the specifications_doc from the draft for some 'user'-edits
+            # this will fail, because we are not allowed to remove the drafts which are already referenced by blueprints
+            with self.assertRaises(Exception) as context:
+                edited_draft_specifications_doc = client.get_schedulingunit_draft_specifications_doc(scheduling_unit_draft['id'])
+                # our user wants to wipe the draft
+                edited_draft_specifications_doc['tasks'] = {}
+                edited_draft_specifications_doc['task_relations'] = []
+                edited_draft_specifications_doc['task_scheduling_relations'] = []
+                scheduling_unit_draft = client.update_task_graph_from_specifications_doc(scheduling_unit_draft['id'], edited_draft_specifications_doc)
+            self.assertTrue('Cannot delete some instances of model' in str(context.exception))
+
+            # but we can create a copy (which has no references anymore to blueprints), and edit this copy
+            scheduling_unit_draft = client.copy_scheduling_unit_draft(scheduling_unit_draft['id'])
             edited_draft_specifications_doc = client.get_schedulingunit_draft_specifications_doc(scheduling_unit_draft['id'])
-            # our user wants to wipe the draft
             edited_draft_specifications_doc['tasks'] = {}
             edited_draft_specifications_doc['task_relations'] = []
             edited_draft_specifications_doc['task_scheduling_relations'] = []
-            scheduling_unit_draft = client.update_task_graph_from_specifications_doc(scheduling_unit_draft['id'], edited_draft_specifications_doc)
+            scheduling_unit_draft = client.update_task_graph_from_specifications_doc(scheduling_unit_draft['id'],
+                                                                                     edited_draft_specifications_doc)
 
-            # check: the draft should have no tasks any more
+            # check: the draft(copy) should have no tasks any more
             self.assertEqual(0, len(scheduling_unit_draft['task_drafts']))
             self.assertEqual(edited_draft_specifications_doc, client.get_schedulingunit_draft_specifications_doc(scheduling_unit_draft['id']))
             self.assertNotEqual(original_draft_specifications_doc, client.get_schedulingunit_draft_specifications_doc(scheduling_unit_draft['id']))
 
-            # but the scheduling_unit_blueprint should still have it's tasks,
-            scheduling_unit_blueprint = client.get_schedulingunit_blueprint(scheduling_unit_blueprint['id'], extended=True)
-            self.assertTrue(len(scheduling_unit_blueprint['task_blueprints']) > 0)
-            # and the freshly exported specifications_doc should still be equal to the original
-            self.assertEqual(original_blueprint_specifications_doc, client.get_schedulingunit_blueprint_specifications_doc(scheduling_unit_draft['id']))
-            # and the exported specifications_doc should NOT be equal anymore to the draft
-            self.assertNotEqual(client.get_schedulingunit_draft_specifications_doc(scheduling_unit_draft['id']),
-                                client.get_schedulingunit_blueprint_specifications_doc(scheduling_unit_blueprint['id']))
-
-            #  check that each task_blueprint should now has a null reference to its delete draft
-            for task_blueprint in scheduling_unit_blueprint['task_blueprints']:
-                self.assertIsNone(task_blueprint['draft'])
-
 
             # -----------------------------------------------------------------------------
             # use the specifications_doc from the draft to make later 'user'-edits possible.
@@ -539,7 +538,7 @@ class SchedulingUnitBlueprintIndirectModificationsTestCase(unittest.TestCase):
             client.update_task_blueprints_and_subtasks_graph_from_draft(scheduling_unit_blueprint['id'])
 
             # ...fetch updates, and check that indeed nothing changed (compared to the original draft/blueprint)
-            scheduling_unit_draft = client.get_schedulingunit_draft(scheduling_unit_draft['id'], extended=False)
+            scheduling_unit_draft = client.get_schedulingunit_draft(scheduling_unit_blueprint['draft_id'], extended=False)
             scheduling_unit_blueprint = client.get_schedulingunit_blueprint(scheduling_unit_blueprint['id'], extended=True)
 
             # check that we have some tasks again