The difference between having an animation and not having such is that when you want to implement the animation, you should provide end bounds as well along with the other parameters. In ordre to get teh bounds of the tooltip, we actually show it for a very little time, get the bounds and then show it with the animation - this happens very fast and that is why you do not actually see it but in fact this a second show of the tooltip and not the very first one. If you want you can try the same logic - I prepared a test demo but unforunately I cannot reproduce the issue there and thus I cannot give you a working implementation of the above explained. If you can help me reproduce the problem, I could try to mimic the same logic in it. However, we recommend to better set explicit size to the RadToolTipManager. Another solution is hook up the OnClientResponseEnd event and set the desired calculated size there.
the Telerik team