First of all, I would like to thank the author of this awesome plug-in!
Now, I use a form with radio buttons with the "default:" argument.
The form works just fine at first, the default button is set just as planned. But after sending a first message, the radio buttons are not set anymore on the default value, no button is set.
I can then send a second, third, 4th... form messages, using no radio button.
It would be nice if the radio button had an obligatory option radio* just like the other types of field, or at least make the default button being set again after sending a first message.