I tried to reproduce the problem with the latest available version of RadControls (2013.3.1015), but to no avail. Please review the attached clip, in which I am showing a button, which is set with the provided configuration and on my end seem to work as expected.
If you need further assistance on this, please get back to me with more details about the following matters:
Are there any additional customization used with the button?
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Let me first answer to your questions:
<...Are there any additional customization used with the button?...> - No customization
I'm using the Q3 2012 version of the Telerik framework.
I managed to fix this by setting CausesValidation="false" and AutoPostBack="false" then implementing a JS function on the client side for the OnClientClicked handler: