Actually, it would be a huge deal to us if it were a bug, as we use a lot of kit items (probably about 3/4 of our SOs include Kit items).
 
I suspect it has something to do with the way the questions were answered in SO-E, and maybe whether it had had been a backordered item initially. There is definitely a way to make it work on a "normal" basis - you just may have to do some playing around to figure it out (that's what the SandBox is for). There have been some problems with releasing Kit items but only in a few rare situations, but as far as I know they are all fixed with the latest update from ISTechSupport.
 
If you're not a subscriber, you may find it interesting that DBA just sent me a fix for the kit release problem in SO-E as well. I think that if you just email Cindy at DBA cdougherty@dbasoftware.com and tell her you're having a problem with releasing kit items she'll send it to you. Or I'd be happy to email it to you as well (I'm using the IST one, but I tested the DBA one and it seems to work just as well).

I suppose there's the possibility that you've discovered one more bug, because of the way you operate. I thought we had probably pretty well covered all the bases, but you never know. I'll be interested to know if the update fixes it for you.