Alright I'm going to post basically the same thing here and in the bug thread with a bit more detail. I went out and looked for a bunch of sneaky cheating Stealth spamming monsters. This is what I found.
The Dark Creepers, will Stealth EVERY time you click on them to target them. Instantly, Every Single Click, they Stealth, then Sneak attack you for upwards of 20 points a hit.
The Undead Gremishka, Same thing. Target them they Stealth. TURN them, they Stealth. Hit them with KD, they Stealth Flat on their Back.
It's one thing if these little bastards get out of your field of view, stealth, come back and nail you, but I was duking it out with three Dark Creepers, and they would Vanish, the second I clicked on them, and I could make them vanish in whatever order I wanted. Even at a +7 initiative modifier, (and maxing the roll more then once), the second that pointer clicked on the target, the little bastard HiPs on you. Toss on 90% concealment in on that it gets worse, since if you Hit them while they are Concealed, they HIPS.
This is not the way this is supposed to work. Oh, casting light on them, does nothing. But make them Hips.
Scale this up to the really hard hitting monsters (some of the Ninja Hook Horrors, the Shades) and you get a big bowl of WTF?!
~Rex