I've personally seen a mounting plate attached sling move the plate and release the detent which went and got stuck in the trigger group, shutting down the gun. It happened to a forum member in Biloxi. So while convenient, I think it's an unnecessary risk when there are plenty of other places to put a sling mount.
I have to wonder if the castle nut was properly staked or the mount was just too thick....which then makes me wonder if the buffer tube was installed properly....the stock had to be canted pretty good right before that happened too.