When I was on 6.x-1.0, I was being hit by the 'illegal choice' error when trying to save a tweaked form. I tried the upgrade to 6.x-2.x-dev and seems to have solved the issue. Any clues why this could have been happening in the earlier release?

The dev. release is quite a nice improvement. Hope to grab the prod release soon!

Thanks for this very useful, helpful module!