I have the same problem, did you find the reason
why it didn't work or is it still an open point for you ?
name attribute is mandatory.
I added the name attribute and this made no difference. I had to physically set the assignTo binding myself within the ActionListener, by examining the event.getComponent.getChildrend().get(0) child component and examining it's getValue().
This is very weird, because I am using the assignTo in other places and it works fine. Only in this case was in not working.