That is because you actually do leave shadows, so the shadows only last for the remainder of the round.
Then how can I pickpocket without leaving the shadows. Clicking on the thieving button when the character is in shadow automatic means leaving shadow.
I think this was the same problem after all:
My link
Ok, I have compared the vanilla BG and BG with Tobex default again.
I think i have missunderstood this hack. Am I right when I say that in Vanilla if you pickpocketing out of shadows you get visible imediately and with tobex you still remain in shadows until the round ends if the pickpocket was succesful ?