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First I ever hear of a stamina bug. As for the key, that kind of thing is possible I suppose (I had an incident in dungeon 2 where a switch wouldn't flip, blocking all progress) Though it IS common for people to get stuck in the first dungeon because of the fake wall nonsense, but I have no way of knowing if you did that or not.
I think it's a bit of a shame that you deleted the game, since this sort of thing tends to get sorted out by quitting and loading a save, but there's plenty of other stuff to play.