First happened on a similar situation, where I didn't have direct LoS with the meany. If I hurl the bomb and it its a wall first, I don't lose mana, I don't get the cooldown and I do lose the gem though. In the above situation it wouldn't be too helpful, but if I do this:
... then it is useful.
I tried playing around with the bug and sometimes the mob will notice me and start chasing me, then the spell would be effectively used (mana+cooldown), but if it's coming down a corridor to me and I throw a bomb into a wall, the bug pops out again.
I can't seem to fully understand when it works and when it doesn't, it feels kinda random. And it's the first time that's happening now, I had similar situations in the other dungeons and it's just happening now.
EDIT: I just noticed that in fact the turn is not going through. In some situations I can throw as many bombs I want not making an action at all.
