Sounds like the beveled surface of the mag catch may have developed a burr or rough spot.
Remove the catch and visually inspect the beveled area on the lower right side (just below the little shelf that serves as the actual locking mechanism) for obvious marks or rough spots. This beveled area should be smooth since the mags use it as a surface to push against and depress the catch during insertion. I polish mine to a mirror finish in this area.
I also change the springs on mine to a little lighter one so the catch is more easily depressed. Depending on your shooting style, this can induce premature mag release if you bump the catch during firing but I use high thumbs and it doesn't present a problem for me. It makes seating and releasing mags much easier.
You may also want to check your mags for a sharp edge at the point where they contact the beveled surface of the catch. A little polishing there doesn't hurt either.
Mikey
