Problem solved. Evidently the oringinal owner had replaced the slide lock/release lever and not with the right one.
The dealer replaced the lever with basicly the same one. One of the dealers employees is a Glock expert and spotted it right away. He put in an original factory lever and no more problem. The rounds in the mag were actually tripping the lever. Ran quite a few rounds of hardball and HP to make sure. I needed the practice anyway and I had to be sure the HP rounds would function reliably. I learned quite a bit from this and I definately need more practice. It has been a while since I shot a light weight 45.