Random grenade throw glitch while firing.

[FakeSympathy]

I am getting this annoying glitch/bug.

When I am using any types of gun that fires full-auto rounds, my guy randomly throws grenade.

This of course makes me stop firing at an enemy getting myself killed. Not only does this make me retarded, but also ♥♥♥♥♥ up the killing spree ( I was on a 25th kill when it happened, killing me).

Has anyone encountered this before?