Here are two save sets.
In the earlier set, detection seems to be working.
A big mud nasty detected me when I was behind him — but this was outside and the worst problems seem to be inside. So I can't be totally sure.
In the second save set, I'm in Pirate Grotto and, when in sneak mode, I can pretty much throw a barmitzvah in front of enemies and they're oblivious.
As soon as I stand up or touch them, they attack.
I tried this location both with normal sneak (level 27, sneak 33), and with my sneak values nerfed using console (sneak 0).
Same results.
Who knows, maybe I've done something to pooch the game. But I've doen very little intrusion (no mods, and I've only used console for a few instances like using "tcl" to get out of polygon traps.
Cheers and many thanks
Tom