weapon fire selector will automatically switch to semi

I have a similar issue except my L3 won't unbind to L3 so everytime you sprint. You keep switching it back and forth. And so when it comes time to shoot you expect full auto but you get semi. Idk why..if I wanted a semi auto..I'd choose one..why have every gun a semi auto makes or have the ability to change it completely. There is no option to unbind it. Just add another bind.