In the Yuan-Ti temple I have replayed the finale with Mershaulk at least 5 times, because every time my character cracks the shield on the Demonstone, the game fails to recognize it. I end up standing around with Mershaulk still very much active and my characters unable to advance.

I have tried searching other forums but there's not even a report of this happening elsewhere. Any help would be greatly appreciated.

I don't know, never been stuck like this... anyway I always used the Beans to destroy it