Okay I have seen this happen once now where my opponent couldnt attack me after his barbarian got a bard buff (even though he didnt sprint). And now I've witnessed it first hand on my end. Bard's buff sometimes shades out the barbs attack icon even though he hasnt attacked or sprinted. I used a different spell because of this, (reposition) not much use if the barb cant attack. But just out of curiosity I left the game (i was playing async) and came back and sure enough the attack icon was available, but it was too late at that point because I had already used an alternative spell and the barb wasnt in range. Anyone else experiencing this? It doesnt happen all the time so it might be hit or miss.
I do the BB combo all the time and have yet to see it. Could happen soon, but not yet.
I had this happen to my sorceress who I gave a bard buff to. Don't ask me why I gave it to her, but I did and it took my attack away.
If it does happen, leave and come back and that tends to fix it. That way you won't lose your turn.