Hello Kishor Dalwadi,
I could not completely understand your exact scenario but as far as I understood you have a button inside the tooltip which performs a postback. If so, the expected behavior is that the tooltip will be closed when the page loads after the postback since teh tooltip object is created and shown on the client and it has been disposed on the postback. The best solution for this case is to simply wrap the content of the tooltip inside an update panel - this will not only keep teh tooltip but will also make your page faster since you will replace the postback with an AJAX request.
If you need further assistance, please provide more detailed explanations and some relevant source code and I will do my best to help.
the Telerik team
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