When I have stacks of ammo in my inventory and I empty a box of ammo or a magazine the stacks will sometimes lose ammo.
The stack will either lose some of the rounds, like 30 stack going to 10 or 20 or will lose all of the ammo and the stack will be in my inventory still, but says it contains 0 rounds.
I have even seen this happen to stacks that are inside of an ammo can.
Have loose ammo stacks in your inventory, unload a box of ammo of the same type, or a magazine (might need to be a full mag), loose ammo disappears.
Doesn't happen every time, but has been happening to me with a fair amount of frequency as of late.
This is totally different from the empty magazine out side your inventory bug.
I have had two ammo cans in my inventory for a while now. I don't know if that has anything to do with this or not.
I have observed this happening with 5.56 and 45ACP, might happen with all but I am not sure.