Thanks a lot for this detailed report of yours. I haven’t heard about this kind of behaviour before, but I do suspect it to be related to certain experiences reported by other Windows tablet or touch screen users.
Could you please try the following:
Find the file “qt.conf” (probably here C:\Program Files\Animation Paper\qt.conf). Delete it or rename it (to save it). Then launch Animation Paper again.
This will force Animation Paper to use Windows Ink. Maybe that will make a positive difference?
Please let me know!