Glock mags with large feeding lips

[gregarat]

I just bought a 15rnd mag for my Glock 19. I then went home to try it. The mag fit perfectly into the recever, but the slide would not drop.
I took out the mag and compaired it to one of the 10rd Clinton clips. I found that the feeding lip on my 15rd mag had abit more plastic matirial on it. This "bump" is preventing the slide relese from being pressed in.
Is this common for 9mm Glock mags? Is their any way I can fix the mag?