Okay, I was wrong [img]smile.gif[/img] You actually
can loot the treasury in the palace. I did so myself with my main character, a level 8 thief with at least 100% lockpick. Nothing about magic wards or anything, just regular locks.
Not that there is a lot to steal, the duchy must've had a hard time. There's somewhat over 1000 gold and some jewels which, together, are worth a lot more, a large shield +1, and some other not that special items.
And stealing all the treasure has no effect on anything but your inventory and gold amount, so don't expect too much