If we understand correctly, showing of the tooltip somehow causes the page to post back. This is not the default tooltip's behavior, so in order for this to happen, you must have written some additional code that is not provided here.
Secondly, if no AJAX is used in the whole scenario, then it is not possible to have the user control added over and over multiple times for each postback, because each postback starts the page lifecycle and the page control hyerarchy "from scratch" - thus it will only load the dynamically added control once for each page invocation, and this is not a cumulative action. So, it is possible that you use some kind of AJAX functionality (again no information provided about it)
Since we are not sure what the problem is, and what the end result should be, my suggestion would be to open a support ticket and send us a sample project demonstrating what you have done, as well as explanations what you want to prevent from happenning.
the Telerik team