I had finished a quest and received The Smoking Gun reward which says: “Your minions have +5 Attack.”
I played Baron Rivendare and after that I played Uther The Lighbringer choosing Baron to receive his battlecry.
The bug is that Baron only had 15/15 after the battlecry ended and entering the combat phase. It never had the +5 attack from the reward until the next recruit phase (but it was too late since it was last turn)
Regards.
EDIT: I also noticed that the same thing happens if you have a Legion Overseer on the field and you play Uther on one of the minions in the tavern, it will only be as 15/15 without the seer addition.