It may well be your grip. I was taught to shoot both thumbs forward; but I end up with both thumbs forward and pointed up a bit - 10% of the time I'm riding the slide release with my right (shooting hand) thumb. I'm working on modifying my grip to put right thumb over the outside of the left to avoid all slide releases...including if I'm fortunate enough one to day to find one...a P30 LEM 9mm.
The USP release sticks out quite far...nice for some things, not so nice for some thumbs forward grips. I think the P30 has the "worst reputation" for thumbs and slide release though.