Smugglers beware.
This happened in the forgotten floor. I got the quest just before entering, and then got a message saying the deimaginator was on my tail. I wasn't quite expecting it to follow me to a hidden spot, so I was a little disappointed cause I wanted to explore, but when he failed to show up, I relaxed. Then, checking out the very last feature before the exit, I saw him up there, not even moving. Just watching...and waiting...
...and forgetting that he can't jump down from platforms :P