When you log-off with gun in your hands and you have another on your shoulder, after relogin, you have free hands and both guns and the second one which was in your hands is now nowhere,but still can be used..
But after you use another gun from shoulder or something else what need hands to be used, the gun from nowhere just drop down and stay on the ground.. So it can be just problem, when someone stops you and say you to drop all weapons, but you still will have this weapon in some imaginary inventory spot {F30007}