So, this is a strange modding conflict I've encountered. While using either set for AMCAR from Vanilla Mod Pack or "A bunch of exclusive sets" - upper receiver just floats. Funny thing is - it's a receiver from the set itself, because default AMCAR receiver is still there. Is there any solution for this? I can use sights as a workaround and it will also set receiver from exclusive in place, so I believe this bug has something to do with sights.

I don't have issue with exclusive sets in any other weapon, including CAR-4.