Possible issue - Component value missing from Form POST via AjaxSubmit after Ajax'd DropDownChoice?

Hi,
I've not had a chance to try reproduce this with a QuickStart yet,
so this is just a post in case it's something obvious I'm
overlooking...

I'm using v6.10.0, and have a page with a form with 4 DropDownChoices
and a Button, with which I use an AjaxSubmitLink.

If I just use them as described, then all works as expected, but if I
add the code to update DDC4's model depending upon the value of DDC3,
using the AjaxFormUpdatingComponent (or whatever it is), then I see
DDC4's choices change as expected, but when I submitted the form,
DDC4's selected value wasn't being set and was set to null in the
underlying object (accessed via a PropertyModel).

A bit of digging seemed to show that it wasn't being passed in the
POST from the browser (while the other 3 values were), but that's as
far as I could investigate as I needed to leave for the day, but I
thought I'd ask if anyone had seen anything similar?

Note that commenting out DDC3's Ajax behaviour and giving DDC4 a
static list of choices resulted in all 4 values being available in the
AjaxSubmitLink callback, so I'm ruling out anything with the
Model/Object configuration...

/Gwyn