Here is the issue with the treant i talked about earlier, was only able to get photos though as i was attempting it in practice mode. The bug occurred on the second try i had with the treant in the starting hand.
As you can see from the images, the ghost cant attack, and both allies and enemy units pass through the ghost. However the ghost will move along with friendlies that head up the line, stopping at the midway point (maximum spawn area). My guess is that the card is in a half spawn state, where the system registers its been played, but possibly due to a mistiming issue where the player is in between having enough mana and not having enough mana, doesn’t actually subtract mana (as can be seen in the first image) or summon the minion. In later images there are gaps between the cards in hand and it appears the system treats those gaps as cards (probably an issue cause by the ghost), apparent from the way it prompts you to bin a card in order to fully draw 2.
As milan majetic said before, the same issue appears with the nature gurdian. However this one might be much more rare as i’ve only ever experienced it once.