If you try playing a WAD with Voodoo dolls with a WAD that uses an Enter Global ACS script, you get multiple occurances of an item. (Kaiser's Heretic Community Chest E1M5, with Heretech in the screenshot)
Normally this would be benign but on picking up ammo for the weapon in question, it goes to the wrong item:
Note how my ammo count still says 50 even though I've picked up the relevent ammo.