No, I wouldn't call it frustrating, just puzzling.
The scenario that played out was this:
There was a creature in a 10 wide corridor that opened up to a room where there were a couple characters.
One of the characters seals off the opening to the corridor with Wall of Stone. The creature on the other side doesn't much appreciate this and proceeds with a full attack routine on the wall that leaves the right half destroyed and the left half with 6 hit points.
The next round the creature unleashes a 30 cone of acid into the room from 5' back from the wall. The template is cut down the middle, one half impacting the weakened wall and the other side spraying into the room. The breath weapon does 30 points of damage.
So the wall is stone and takes half damage from the acid (15). Then we applied the hardness of 8 (Stone) and the remaining 7 points of damage destroy that half of the wall with one point left over.
Our question was what happens next? Do the characters that were previously shielded by the wall take 30 points of acid? 1 point of acid? No damage?
At the time we went with the full 30 as the acid blew through the cracks and dissolved the wall, but I wasn't sure that was the correct ruling.