It seems that when charging the grenade in tesselation, if you don't shoot right away and instead switch weapons, when you switch back the gun will have no ammo in the mag and you're unable to shoot or reload. The gun completely breaks and become unusable, forcing you to take it off and back on to be able to use it again. I don't know if you're supposed to lose the charged shot when switching weapon or not but its definitely not working properly.