The mags should seat regardless of whether they are loaded.
I have the same gun and I noticed the mag release kinda sucks.. What I noticed is if you look at the button itself, there is a screw in it that holds it onto the main release lever. If you take it apart and put the button on one way, it will bind up and stuff, but if you flip it around and put it back on, it will work perfectly. I just put a little mark on the side of mine so I know which way to put it on when I am reassembling the gun. I guess the hole is just a little off center or something..