Hello lnu,
I built up a test demo based on your explanations and also tested the provided HTML and I can confirm that I reproduced the behavior you report. However, this is expected behavior since what happens is teh way the things work. When you mouseover (or fire another event) the link, it raises its mouseover event which is bubbled and raises the mouseover event of teh parent element which is the TH. You can easily confirm this by using only standard HTML element and javascript without using RadControls at all. For example, look at the following modification of your sample code:
If you test it, you will see that when you hover the A element, the mouseover event of the parent TH is fired due to teh event bubbling and this is the cause for the problem. You can find more information about event bubbling on the net, e.g below:
http://www.quirksmode.org/js/events_order.html
What we suggest is to keep the things the way they are but in case you really need modifications of the functionality if you specify the exact result you want to achieve we can try to develop some workaround for you if this is possible. However, using such a workaround can cause a problem which in my opinion is not worthy to risk since the problem with the tooltipified arrow is not that serious.
Sincerely yours,
Svetlina
the Telerik team