If the slide is locking to the rear when you are firing (after each round) than the problem is a broken slide stop. The slide stop is retained into the frame by a pin. If you have removed the pin and then reinstalled it than it is possible to "snip" the end of the spring off. If you do this than the natural tendency of the slide stop is to "ride up" thus causing the slide to lock open. Normally if you break down the gun than it will not affect this piece however, it is possible to break them over time. Rest assured that it is a relatively easy fix and with a nail punch and the replacement part I could walk you through it over the internet if you would like.
Enslosed is a picture of the slide stop. This one is by Glockmeister and I highly reccomend it.....but I digress. Look at the tublar piece of metal that extends from the slide stop. This is the slide stop spring and it rests under the frame pin to create tension for the slide stop to work. I would bet that if you removed it, it would be shorter than these. If you can get your hands on one, or order one of these, they are easy to install. If you need help let me know......hope this answers your question.
norfdet893- who knows more about Glocks than he does about KT's