Confirmed.
A friend of mine had the exact same problem. He called me on the phone for help, but sadly there was nothing i could do for him. :-(
At first he couldn't enter the lava. ("You can't.") Maybe he wore the gothic boots, he had found one gothic item, but we discussed knockback, so probably he didn't even wear it. Does lava slow you down so the gothic boots imobilize you when you try to walk on it?!
He also then did a rocketjump, catapulting him next to the wall. From there he couldn't get back onto the islands anymore, even tried a normal rocket against the wall. Unable to jump downward again, he was obviously doomed to starve in the lava as soon as the envirosuit would wear out (No phase devices were accesible at the time either). Desperately he reached some more enemies and leveled up for the last time. So he became a fireangel went of in a thermonuclear blast.
I will ask him to post for the mortem if it helps. And the story isn't so sad, because one day later he called to announce his first killing of the cyberdemon.