When editing a tune with an upbeat, changing the length eats up strokes #130
Description
Reproduce : in Compose, open a tune with an upbeat, like Angela Davis - Break 1 :
Change length to 8: you can see the first beat (that was in position 0) has been "eaten". The beat that used to be in position 1 is now in position 0, and all following beats have shifted:
Change length back to 4: the same thing happens again, a second beat is "eaten":
