I'm playing the GOG version (no patches).

I'm making the journey from Moonshade back to the mainland via furnace. I found the gargoyle city, passed the test, and got the serpent ring and black rock key. I also found a serpents tooth in the city.

After getting the black rock key, I opened a door to a teleporter which leads to a fiery room with a serpent gate which I recognize from when I first got the jawbone from the Mad Mage. I activated the serpent gate and as usual was taken to void where the portals to various places are. Since I found a new serpents tooth, I figured that another door would be open, allowing me access to another portal, but that was not the case. Only 4 doors/portals were open even though I have 5 serpents teeth including the one I just found.

I went back into the Gargoyle city and talked to the head guy there and he opened up a passage for me to leave the city. After fighting some trolls I found a serpents staff, so it seem like that was the right route to take and my impression is if I keep following the caverns to the west I'll eventually get to the mainland.

However, I am still wondering what's up with the serpents tooth I found the gargoyle city. Is it normal at this point that I didn't get access to a new portal?

I'm guessing maybe the game doesn't open up access to another portal just yet to keep the player on the correct path, but this whole area of the game seemed horribly glitchy, so I thought I'd ask before going much further.

Thanks much for any insight anyone has!

Apparently not - I went back and put my nose against each closed door and one of them opened! Thank you! Thanks for the info!