Brian - One of the problems is that you aren't keeping your hand behind the ball either. It's on top of it like you're holding on to a handle. At the point of release your hand should be more in a position to push the ball towards the arrows, not slide something that has a handle. See if you can get the feel for that difference.
I've been working on this particular issue for the last few weeks and I believe I have it under control now. I started cupping my wrist a little to try and keep my hand behind the ball more. Now I'm almost under the ball and am no longer sliding it out there like a suit case.. If I can remember to bring my camera out next practice I'll take another video for comparison. Since I have been doing that I have not had any more issues with it tracking over the thumb hole.
Although the only caveat that I am seeing with cupping my wrist is that it is causing me to have a lot more hook and causing me to play further left. Which in it's own is fine I can play anywhere on the lane that I need too, but I am losing my pin carry. It's kind of hard to explain, but when the ball hits the pins it's like the pins just fall over, there is not any mixing going on. Does that make sense?