I dragged Deathsprout onto the field to play it, but did not have the correct mana, so cancelled. One of my opponent's cards in hands was then showing as Deathsprout for most of the rest of the match. This only stopped when they discarded cards to go to 0 cards in hand. When that happened, the cards they discarded seemed to go to my graveyard, but that fixed itself when I clicked on my graveyard to get a detailed look.