tony, i think you're supposed to send stuff through the commandline.
Ok, psethura, i tried it, and i see your point...
The java api says this:
Exactly one check box button in a CheckboxGroup can be in the "on" state at any given time. Pushing any button sets its state to "on" and forces any other button that is in the "on" state into the "off" state.
So, i don't think it's really clear whether the one-at-a-time rule should be used always, or just when someone pushes a radiobutton. On the other hand, the radiobuttons behave quite weird when you use them at first, so perhaps something is wrong.