Most probably the problem comes from the fact that you only add the button as a response to some event and then you are not recreating it on postback. That is the reason why it vanishes when button is clicked.
When you are using dynamically generated control, you must make sure that the control is recreated on every postback. You could check this
great article from the Infinities Loop blog for more information on using dynamic controls.
the Telerik team
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