I found another bug with ruined ammo. If you "split" the ammo it will give you two new piles of ammo, one Pristine and one Ruined. You can continue to split the ammo until all but one bullet is Pristine.

No screenshot but an example:
Split 20 ruined bullets = 10 ruined and 10 pristine.
Split the 10 ruined bullets = 5 ruined and 5 more pristine.
Split the 5 ruined bullets = 2 ruined and 3 more pristine.
Split the last 2 ruined bullets = 1 ruined and 1 pristine.

You can then combine all the pristine ammo and be back at the original amount of ruined ammo minus 1 bullet.