ToME: the Tales of Maj'Eyal

I've cleaned all other dungeons which able to trig escort quest and going to dreadfell.
At lvl8 i still have only 8 of them. After opening vaults at lvl8 i've met radiant horror lvl ~55 being only 33 myself.
After several unsuccessful tries and i've decided to have a pause and to return to lvl7.
And then surprise! Lone alchemist at the exit from cleared level has appeared along with his portal!
Quest has been finished, all right, but the situation is quite strange.
My first nightmare char by the way.

This is known behaviour and I don't know if it's a bug or intentional.
I don't know all the details, but this is what I understand: The game decides in advance what levels the escort quests will be on. When you load one of the levels, the escort will start next to you, and the game decides where the portal will go. But if the route from the escort start to the portal location has to go through a closed door, then the game will think the path is blocked and the escort can't reach the goal, so it won't spawn the escort. If you open the door(s) and come back to the level later, then there will be an unobstructed path, so the escort will spawn.

For future characters, note that escorts can also spawn on Reknor floors 1 and 2, which come after Dreadfell.