That's not a bug, that's how it is supposed to work.
The part in your description that reads
assign token to a card.
involves moving the Teacher from the Tavern mat back into play, so it gets discarded, shuffled into your deck and your draw it some time later.
The start if the relevant ability reads
At the start of your turn, you may call this
, to move your +1 Card,...
"you may call this" means to put the Teacher back in play, as you do with almost all Reserve cards when your use them.