Found in GWT Release (e.g. 1.5.3, 1.6 RC):

1.6

Encountered on OS / Browser (e.g. WinXP, IE6-7, FF3):

all

Detailed description (please be as specific as possible):

Make a radio button and give it a ValueChangeHandler.
Click it.
No value change events fire.

Workaround if you have one:

Add a ClickHandler and the ValueChangeHandler will start to work.

Problem is that I forgot to sink click events. Didn't notice because in my
manual test app I had added ClickHandlers, and doing that has the side
effect of sinking them. 

Links to relevant GWT Developer Forum posts: