When wearing skulls, such as a creeper head, or a wither skeleton head, which my server allows, I found that if you repeatedly take the skull off, and put it back on again, basically clicking as quickly as possible, the skull will multiply to another, which can then be tossed down, or moved to regular inventory. Basically, one skull would remain on the player head, while the other would be "selected," as if you picked it up out of the inventory. I was able to reproduce this in survival.