Originally Posted by eltee
It's very likely that your thumb is sometimes bumping the slide lock lever. I have mine radiused at the end to prevent this.
This is an interesting comment. The MK40 does feel different in my hand from the Glock 23 I am use to. I will make sure the next time I go shooting, I am very aware of where the slide lock is. Although I think if I was bumping the slide lock, it would happen more than 3 times in 100 rounds.