While playing Diablo 3, my Wizard found a Black Mushroom on her first run-through of the Cathedral. I was totally stoked, of course, but then when I was playing with my Monk, another Black Mushroom spawned on his run-through.
At first I was excited, but then I was just really confused. Since you only ever need one Black Mushroom, and can't really get rid of one, why did two spawn? Is this a bug, or is there some purpose to it? I've included a screenshot of my Stash as evidence.