Revianne's mage has (infinite) contingency Stoneskin

Just had an extremely tough fix with Revianne's crew coming after Jaheira. The outrageously hard part was the mage with a contingency Stoneskin popping up *every* time he was damaged. Whenever one stoneskin was downed, another (almost) immediately replaced it with another contingency. I counted at least 10 such contingencies firing, which I am pretty sure is not intended for a party at this level. My own party was still mostly 8th/9th, using basic weapons (and I quickly lost half of them). I managed to power my way through, mostly as my lead character has Grandmaster darts, so was single-handedly downing the stoneskin most rounds (after I had finally dealt with the rest of Revianne's group).
Sorry - no save game as it is kind of tricky to make a save after a fight starts
Sorry - no save game as it is kind of tricky to make a save after a fight starts

0
Comments
Should mention I am using the Mac App store version of the game which has not yet been patched, but I don't see this issue in the patch list, I am not sure if that is relevant.