Perform the steps mentioned above!
I haven`t tried whether this duplication also occurs to other magazines for M4 or to magazines of other weapons.
I haven`t tried whether this duplication also occurs if another backpack is used or if the Protector case is somewhere else in your cloth (NOT in the backpack).
I haven`t tried whether this duplication also occurs if the magazine inside the Protector case isn`t fully loaded (less than or equal 59 rounds/bullets).