Game Mechanics: Sneak fails and spell Los

[Tecmos Deception]

Perhaps related, perhaps not. I don't know. But every time my rogue is in OT outpost (where he is kos) and I use sneak to access some of the vendors there, the next hide and sneak I attempt after leaving that vendor inevitably fail.

I get the success messages, but I am still, apparently, visible to mobs from the front and/or the back.