OK, it would appear the GM lied to me. I was just killed, yet again, by a Judicator Demon in Uleg. Range through Sneak and Invis as well as this time Deoderise.
Two questions arise - I think that on every occasion I had earlier slept a Tauri type mob and re-sneaked and inv before running away - would this cause this behaviour?
Second, could the mob be true-sight / true-sound?