Insert Mode by mouse broken:
This mode is mostly adopted by basic pc editors and tablet and mobile applications. It is part of Avid which has same as Kdenlive 3 different modes to use the mouse, too.
The idea is that you can't let space on the timeline. So when you move a clip in the timeline or you delete it the following clips in the track collapse as when you perform an extract operation by the keys. As the mode is related to the use of the mouse only the tracks involved by the operation are affected and the Timeline-head buttons, except for the lock, are ignored.
If you move a clip from one track to another, the first track (from where you remove the piece) will collapse the gap like during a normal Extract operation. The second track (to where you put the piece) will split as it happens during a normal Insert operation. All the other tracks remain untouched.
By now only the Insert operation works but it acts on all the tracks. Extraction is ignored. In the version before the refactoring, the extraction operation was ignored as well, but the operation was performed only on the touched track.
As the 3 modes by the mouse are complementary I think we should fix it because, in my opinion, it is not very usable by now.