I was playing a PvP Duel with an unupgraded deck: Ghosts, Nightmares, and Silences. I Nightmared a Ghost, and chained two silences. However, after playing the first Silence, I noticed that my opponent's HP dropped by 10 for just a second then increased by 10 right as his turn ended - right when his full hand had to discard. This was almost instantaneous, and therefore I could not get a screenshot. It happened once again, when I silenced again some turns later (forcing him to discard again).
Chatting afterward, I managed to confirm that 1) Our HP counts matched, regardless of the strange 10 HP-swing, and 2) he never discarded a Ghost during the entire game.
This bug is really just a visual bug and doesn't interfere with gameplay at all, but it would be nice if anyone could confirm seeing it. If an identical report has been submitted already, I might have missed it with search function down.