I bought my first 1911 from a buddy. Ultra Comapct 45. It was a safe queen with about 30 rounds thru it. It is great to shot, but it will not lock open unless there is a clip in it, resulting in a M1 pinky when I was cleaning it. Is this a common problem?
The cut out on the slide could be mismachined or have a burr on it. The slide release may be out of tolerance. At any rate, to be safe I would recommend taking it to a qualified smith.
If you're still having any problems, or fixed the problem, I would be interested to know how you did, or what the original problem was. Hope all is well