Timeline layers should not jump downwards after a bottom layer is twirled closed
This is problematic behavior, because it makes it very easy to lose your place.
Instead, keep the blank space that appears at the bottom:
Don't automatically shift all the layers downwards! Allow the user to scroll up manually (which will move all the layers down.)
Perhaps not everyone will like it this way, (and those people are crazy) so perhaps this should be a preference. Everyone's happy!
If that made no sense, fear not! I have a video: https://youtu.be/9giCThQxcqE