EDIT: For those who don't know, the "Gun Glitch" is the perpetual firing of your weapon without any influence from you.

I actually thought this was common knowledge, but in a few pubs lately, knowledgeable/skilled players have claimed to have had this problem and restarted the game. Just wanted to inform those who don't already know that there is a simple solution for this:

ESC, spectate. Then click on "Join game" or on one of the team icons and hold your click down; you will join in the game and start firing, at which point you can let go for the click button. There, glitch gone.

I'm not an expert, so I could be wrong, but I think inputs in games have two positions, on and off. When off, nothing happens; when on, a designated action happens. In the case of left click, on means the firing of your weapon. Sometimes the game will have your on and off reversed, and you'll stop firing only when you hold the left click button down. You can reset it by restarting the game or you can readjust it manually by affirming that the on position is when you hold the click down.

Sorry if this is all known and I just happened to run into the few people who don't browse the forums ever.

Lol, i always thought it was my Mouse :/

For those who are using laptop there is a quickier solution. When your guns start autofire just hold your left mouse button down and tap touchpad once like you would fire with it.