Do you use wx2.8 or 2.9 ?
If just 2.8, can you try it with 2.9 also ?
Does it happen if the mouse is not moved ?
Does it happen with all tabstyles ?
If you have chosen "Default" as style, does it also happen, with different gtk-styles on your system ?
It might be a broken TabHitTest(), but I don't know how this should happen, because it's also used to show the tooltip, or a broken mouse-motion event or a combination of both.