RadButton peforms a duplicate request (the second request aborts the first one) when the following conditions are met:

-The page is opened from Visual Studio 2008

- A RadButton exists on the page and the form is submitted when a text box is focused and enter key is hit.

-Default button is not set to the form.

-RadButton's UseSubmitBehavior is set to true

-.NET Framework 3.5 is used.

-The browser is Internet Explorer.

The workaround is to either set Default button for the form or set the UseSubmitBehavior property of the RadButton to false.