diff --git a/engine/api.py b/engine/api.py
index b146326..e93e60a 100644
--- a/engine/api.py
+++ b/engine/api.py
@@ -599,9 +599,15 @@ def _reinsertDeletedTrack(track, trackIndex):
     callbacks._numberOfTracksChanged()
 
 def deleteTrack(trackId):
+    """ indirectly calls session.data.buildAllTracks() through group change.
+    This is wasteful, but it acceptable. We let the code stay simple in exchange for redundant
+    re-building of all tracks.
+    """
+
     track = session.data.trackById(trackId)
     if not track: return
     oldIndex = session.data.tracks.index(track)
+
     with session.history.sequence("Delete Track"):
         setTrackGroup(trackId, "") #has it's own undo
         deletedTrack = session.data.deleteTrack(track)
@@ -613,7 +619,9 @@ def deleteTrack(trackId):
             session.history.register(lambda tr=deletedTrack, pos=oldIndex: _reinsertDeletedTrack(tr, pos), descriptionString="Delete Track")
 
     updatePlayback()
-    callbacks._numberOfTracksChanged()
+
+    callbacks._numberOfTracksChanged() #TODO: throws a console error "port not found". but that is not critical.
+
 
 def moveTrack(trackId, newIndex):
     """index is 0 based.
@@ -667,7 +675,7 @@ def setTrackGroup(trackId, groupName:str):
     if not track.group == groupName:
         if not groupName.lower() in (track.sequencerInterface.name.lower() for track in session.data.tracks):
             session.history.register(lambda tr=trackId, v=track.group: setTrackGroup(trackId, v), descriptionString="Track Group")
-            session.data.setGroup(track, groupName) #includes session.data.buildAllTracks()
+            session.data.setGroup(track, groupName) #includes session.data.buildAllTracks(). This is wasteful, but it acceptable. We let the code stay simple in exchange for redundant re-building of all tracks.
             updatePlayback()
         callbacks._numberOfTracksChanged()
 
diff --git a/engine/main.py b/engine/main.py
index 5b5ba37..d8db5f9 100644
--- a/engine/main.py
+++ b/engine/main.py
@@ -290,6 +290,8 @@ class Data(template.engine.sequencer.Score):
             self.sortTracks()
 
             if buildAllTracksAfterwards:
+                #TODO: this could be optimized. Currently everytime you delete a track, even an empty one, all tracks are re-built.
+                #However, it is not *that* important. Everything works, good enough.
                 self.buildAllTracks()
 
     def sortTracks(self):