First I played Educated Elekk and got one of my spells shuffled back into my deck with his Deathrattle; I'm not sure if this part is needed for the bug to bug. At this point HS Decktracker showed me that spell back in my Decklist.
Secondly I played Mischief Maker which swaps the top card of my and my opponents deck, but both players should not know which card the opponent got from their own deck.
Then I watch my decklist while my opponent draws and HS Decktracker actually removes the spell which Educated Elekk created from my deck which is also the spell my opponent drew which I should not have known until he played it.
https://www.reddit.com/r/hearthstone/comments/i8gafq/bug_hearthstone_deck_tracker_revealed_me_my/