it's a very old and a very frequent painter bug;
those cursor marks go away if you quickly zoom in/out, or make any other operation that will make a screen redraw.
For me, switching the tool from brush to eraser (hotkeys B and N respectively) and back did the trick, same thing with hitting tab twice to hide and show menus and panels.
alternatively, disable any kind of brush ghosting, it also worked for me.
on the fourth day of glitchmas my painter™ gave to me
four random crashes, three broken brushes, two system hangups & one corrupted workspace