It totally bricked the run. But it wouldn’t let me advance into the Soul Furnace with the door, it would light up if I moused over it but nothing would happen. I tried porting to town and then used the portal to go back and it dumped me INTO the Soul Furnace but in the wall or something.
At that point I couldn’t do anything, the music was playing like it was the battle and I could see things moving, those big weird shapes in the picture were slowly turning. I opened the portal again but it was pretty clear I was stuck wherever I was. So I had to exit the game and start over.