I already answered your other thread and for your convenience and for others who might have the same issue I pasted it below:
It is possible to get undesired position when there is not explicit width set and the OnAjaxUpdate event is used. However, this is expected behavior in such case - the content of the tooltip is loaded through AJAX and the tooltip cannot "predict" the width it has to have when it is shown. Thus it shows at some coordinates and after that the resize takes place and as a result the position is not the correct.
This being said, you should set the Width property explicitly and to use the ContentScrolling property to the desired value in order to determine the behavior when the width should be bigger than the set. If you want the tooltip to resize accordingly you should set it to Default.
We are currently working on improving this behavior but for the time being some explicit size set is the best solution for the case.
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