>>MouseEnter/MouseLeave don't fire if mouse movement is very fast. Can you test it?
>>
>>MartinaJ
>
>Yes, if I move mouse very quickly between columns, I don't see tooltips. I think I can live with that.

I think the behavior is by design. Just look anywhere (including other OSes), there's always some delay before showing tooltips. If there wasn't, just getting your mouse from one end of the screen to another could fire all the excitement of a minefield.