I believe I had my weapon in combat stance and rolled beneath a wall to get into the area you see in the screenshot (North West Airfield, Barracks South). For information on the pistol, it is the P1, had a 7/8 round loaded mag attached and was always in my hands at that time. I believe I did never Vault in this scenario, nor did I throw the weapon. If i remember correctly, I did not have a backpack at the time, but a pistol holster where I fitted the pistol if I didn't need it. It was easy to fix this problem ingame since I just put the weapon in my inventory and in my hands back again. Afterwards I proceeded to loot the barracks and filled up my canteen at the pump.