Fix handling of new absences cutting existing ones in two halves

aleksis/apps/kolego/models/absence.py

@@ -190,10 +190,12 @@ class Absence(FreeBusy):
                     # First, cut end date of existing one
                     event_within.datetime_end = new_datetime_start
                     event_within.save(skip_overlap_handling=True)
-                    # Then, create new event filling up the remaining time span
+                    # Then, create new event based on existing one filling up the remaining time
                     end_filler_event = event_within
                     end_filler_event.pk = None
                     end_filler_event.id = None
+                    end_filler_event.calendarevent_ptr_id = None
+                    end_filler_event.freebusy_ptr_id = None
                     end_filler_event._state.adding = True
                     end_filler_event.datetime_start = new_datetime_end
                     end_filler_event.datetime_end = event_within_datetime_end