When Young Witch is in the supply, there is no extra supply pile for the bane card to go with it, as far as I can tell.
There is, (it says Bane at the bottom of the pile)
Maybe I just didn't notice it. But I thought that the rules for Young Witch was that it would add an 11th supply card costing from 2-3 as the bane, but there definitely wasn't an extra supply pile for Young Witch when I was playing with it.
Did you count the piles? I have no knowledge of other reports where there was no additional pile and can't reproduce this.
There should be an extra card, but it could also be clearer what the bane is (other than some text at the bottom).
I was certain there were only 10 kingdom cards, but it's possible I missed one. I don't have expansions, but I will post again if this ever happens again to me.