Hello. I've tested this against last development release (got from GitHub) and against stable (in your demos page) using Firefox 3.5 on Mac OS X. Using Safari 4 the problem doesn't appear.

1. Load any table with a few rows
2. Move the mouse to the third or fourth row and stop it there
3. Wait for tooltip to appear
4. Now, move the mouse 1px in any direction

At least with my configuration, the row hovering jumps to two rows above. Not a big deal, but a bit annoying because you always move the mouse more than 1px, and the row jumps back and forth to the current row.

I hope this helps!!