CONTENT IS OUTDATED !
PLEASE CHECK THIS NEWER POST REGARDING THIS ISSUE
I've written an extension to simplify the workaround. I'm not a whiz programmer, so hopefully someone might help me improve this code.
How to use this :
myRadioButtonList.FixAjaxPostbackBug(MyUpdatePanel, AddressOf myFunction)
That's it. The limitation is, you have to call this function everytime in pageload and everytime after u dynamically add items to your radiolistbutton, because the hidden link is dynamically added to the updatepanel.
Works well in IE, Opera, FF (Read up) and I'm happy with it.