Gothic 3 LAGO Mine Slaves

I've taken the slaves to LAGO, but the one that went to the top of the hill doesn't want to come down. I've been pushing him, but he always goes back to where he was.
I've gone back down into the cave and waited but he hasn't returned. What's next?

It's OK, I left the "emaciated slave" in the cave and then I went along the coast hunting "Lurkers". I had enough to complete Mamuk's quest and then I went back to the slave cave and the other slave had come down into the cave. I took the "emaciated slave" to the back of the cave and was able to say "here we are" and "Get to work now."

If it was a nice day and you were in a good mood, you could have freed the slaves. They would have walked across the desert to stay with Yurit their boss (the slaves were nomads) - but the emaciated slave will not join the troop and stays alone in the cave for some reason,