Once we run program, we see visually distored mouse cursor. If we move mouse cursor away from Grafx2 window, then we can see that once real amiga mouse cursor appear on WB screen, cursor in the Grafx2 window looks fine again. Once we make grafx2 window active again, and so we have mouse cursor inside of grafx2 window, it is distored again.
Another helpfull fact, is that if we trying to take screenshot of that distored mouse cursor (i for myself have attached sgrab on the "prntscrn" key, so do not need to move cursor away from programm), then screenshot show that there is good mouse cursor, and not distored ! While visually, it is. What make me think that such kind of problems happens when PIP, or compositing, or some hardware sprite collision involved..
I also attach 2 screenshots where i marked by red area cursor part. One screenhot of how it should be (i.e. how it on win32 for example), and another is aos4 distored version (screenshoted by other device, because as i say, sgrab make screenshoot like there is no distortion at all).
kas1e
commented
6 years ago 
Grafx2: http://os4depot.net/share/graphics/edit/grafx2.lha
Once we run program, we see visually distored mouse cursor. If we move mouse cursor away from Grafx2 window, then we can see that once real amiga mouse cursor appear on WB screen, cursor in the Grafx2 window looks fine again. Once we make grafx2 window active again, and so we have mouse cursor inside of grafx2 window, it is distored again.
Another helpfull fact, is that if we trying to take screenshot of that distored mouse cursor (i for myself have attached sgrab on the "prntscrn" key, so do not need to move cursor away from programm), then screenshot show that there is good mouse cursor, and not distored ! While visually, it is. What make me think that such kind of problems happens when PIP, or compositing, or some hardware sprite collision involved..
I also attach 2 screenshots where i marked by red area cursor part. One screenhot of how it should be (i.e. how it on win32 for example), and another is aos4 distored version (screenshoted by other device, because as i say, sgrab make screenshoot like there is no distortion at all).