Brian,
Hi. There is a longer explanation to why this doesn't work (with radio buttons like checkbox lists) but I think I covered that in a support ticket with you. Either way, with the 2.7 release we added a javascript function call that can be used, I think its called funcRadioCalc. This should be used instead of the checkboxlist client side event. We will work on a demonstration that covers adding radio buttons but it should be easy now that the function call is generating the proper value. Just for reference, you can access this Beta Springs page which uses the function call and gets the radio button value. You can then use this add or calculate multiple radio buttons etc...
Beta Springs - Radio Button Calculation w/ Client Side Events
-Chad