use track instead of score as parent when joining blocks

engine/main.py

@@ -477,6 +477,7 @@ class Data(template.engine.sequencer.Score):
                                     #assert parentBlock, item
                                     #assert parentBlock.parentTrack, (parentBlock, parentBlock.parentTrack)
                                     if parentBlock.parentTrack:
+                                        assert parentBlock.parentTrack in self.tracks, (parentBlock.parentTrack, id(parentBlock.parentTrack), hex(id(parentBlock.parentTrack)))
                                         listOfChangedTrackIds.add(id(parentBlock.parentTrack)) #there are items without parent Tracks. They have None. We must filter them out otherwise our changedTrackIds get polluted with id(None)
                         else:
                             continue
@@ -488,7 +489,6 @@ class Data(template.engine.sequencer.Score):
                 track.toPosition(originalPosition) #has head() in it
                 finalResult.append(result)
 
-            #hier weiter machen. Die ids gehen durcheinander. Es ist nicht nur der assert check. Wenn wir das weglassen kommt das Problem später
             for changedTrId in listOfChangedTrackIds: #It is not the track ids that change but tracks changed and these are their IDs:
                 assert self.trackById(changedTrId) in self.tracks, changedTrId #selecting from hidden or deleted tracks is impossible
 
@@ -641,7 +641,6 @@ class Data(template.engine.sequencer.Score):
 
         Will only delete from visible tracks. No hidden, no deleted.
         """
-
         validSelection, topLeftCursor, bottomRightCursor, listOfChangedTrackIds, *selectedTracksAndItems = self.listOfSelectedItems(removeContentLinkedData = True)
         #selectedTracksAndItems format: [track1[(item, itsKeysig), (item, itsKeysig), (item, itsKeysig)], track2[(item, itsKeysig), (item, itsKeysig), (item, itsKeysig)]]
 
@@ -921,11 +920,12 @@ class Data(template.engine.sequencer.Score):
         #we now have made it clear that the requirements from the docstring are met.
         dictOfTrackIdsWithListOfBlockIds = {}
 
-        protoBlock = startBlock.copy(newParentTrack = self)
+        protoBlock = startBlock.copy(newParentTrack = self.currentTrack())
         protoBlock.data += startFollowUpBlock.data
 
         for firstBlock, secondBlock in workingList:
             parentTrackId = id(firstBlock.parentTrack)
+            assert firstBlock.parentTrack in self.tracks, (firstBlock.parentTrack, id(firstBlock.parentTrack), hex(id(firstBlock.parentTrack)))
 
             if parentTrackId in dictOfTrackIdsWithListOfBlockIds:
                 blockOrder = dictOfTrackIdsWithListOfBlockIds[parentTrackId]