The new functionality with <label wicket:for="..."> (See
WICKET-1469) does not work completely for radio buttons, probably because the referenced Radio instance is no FormComponent but just a LabeledWebmarkupContainer.
The problem is in AutoLabelResolver, line 181:
if (component instanceof FormComponent)
There should be a special case for Radios to get its associated RadioGroup first and use that as component to derive the CSS class from