Button "bouncing" problem?

I am working on a site for my husband’s business. I’ve been doing it for less than a day so it’s not great but I have a problem with the buttons. If you mouseover them then mouseout they might just bounce down and then bounce back up. But occassionally (to recreate, try moving your mouse over them and then back out very slowly over the bottom, so that your mouse is just on the line of the button. See it shaking? It kind of bounces weird.

(PS I just uploaded the SWF because I’m about to be late for work so sorry that it’s so big and crappy!)

Anyone know why it’s doing that (and how to fix it)?

Thanks!
(-: sogj