http://jsfiddle.net/ABGPA/4/

Click on a Radio Button that is part of a group. No radio button in the group is clicked yet. That radio button's click handler contains e.preventDefault().

Expected: That radio button will not become checked after any click, leaving the group "empty".

Result: The clicked radiobutton becomes checked. All further clicks work as expected.

Other note: I don't know if this is expected, but $(this).is(":checked") returns True, even though e.preventDefault() keeps it from retaining its check. I would have expected it never get checked in the first place, rather than become checked, then become unchecked. Could this "set/unset" check be the reason why the first radio button becomes checked-- because the browser doesn't support "clear checks from radio button group"?