I was unable to equip an MP5 onto my back while holding it in my hands. I had to clear up inventory space before being able to properly store the weapon. I came across a rifle that required the primary slot and was unable to store it much like the MP5. I logged out with the MP5 in my backpack and the rifle hands in effort to keep the it and continue playing. Upon reconnecting I found the original an MP5 in my primary weapon slot while a duplicate remains within the backpack. The SKS is still in hand and was stored properly once the original MP5 was dropped.