Vista - RadioButton and IsChecked data binding

I have the following problem: I tried to databind the status of my radio
button through the IsChecked property to a property of a CLR object. I works
well the first time I select the radio button but if I have several radio
buttons in the same group, the uncheck state is never propagated back to my
CLR object. Do you think it is normal ?
By the way, for debugging purpose, I implemented Check and Uncheck event
handlers on each RadioButton and the IsChecked property is reset when the
Unchecked event is raised but the value is not propagated back to the CLR
object.