Factorio Forums

Using the default pause (shift+space) while a flamethrower or a shotgun is equipped will fire that weapon after the pause ends. Not only can this lead to may moments of regret, but it can be very confusing way to come back to the game after a short break!

Shift+space should consume the event.

It is. You're holding space down after you've released the shift key. Don't do that if you don't want it to fire.

So long as you're holding shift pressing space will never fire your gun.