I also noticed sometimes the mag slide gets caught up on the spring as well causing you to lose one or two rounds, because the spring doesn't retract properly. You could eliminate this by shaving the two corners of the mag slide where the spring goes in making it sharper and rounder. this usually happens when you have to pull the spring making it strong enough to load the last couple of rounds.
just thought i should throw this out there if anyone's having this problem too.