Good fun and really mayhem at later levels! I found that my balls would get stuck in the corners if they were in just the right place when the levels reset. The fix for this (the three times it happened) was to create another purple ball, but at some point it's not going to work. They would be stuck there, level after level until making the new purple ball.
Okay, weirdness. I had 5 balls stuck in corners and a few levels later they freed themselves on level reset. I wonder if it's a resolution thing, Firefox under Win10, 1366x768 resolution.