This isn't anyhow related to the flames people are writing about recent
invis+ambush thingies.

I have had an experience with a mob that doesn't see invis (or I atleast
assume that an agro mob that doesn't engage a combat with me when I'm invis
doesn't see me) but it did chain invisibility at itself. After few casts it
actually managed to success in that spell and went invis. At the very moment I
was quite sure that it worked in two ways. The mob itself turned invis AND on
the same time it gained see invis (or atleast I assume that it gained it
because it engaged a combat with me).

Donno if things like this are even possible now, but it was fun to watch.