HTFUDan, it may not be your thumb, it may be like me and my trigger finger. I index my trigger finger high along the side of the slide and I can feel the slide release hitting the 2nd knuckle of that finger. If you can slowly do a reload of your gun and pay strict attention to where your trigger finger is. I never had issues until the 9 and I think it's because it is slightly smaller. Obvisouly the Glocks didn't have the ambi slide release so it wasn't an issue or something to watch out for.