Does the Unique bug apply to every item you have in your bank?
I have (very nearly had, in the past tense) a Blue Bracer of Control - which I only have one of. Yet, when I picked up the bag containing that and two other non-unique items, I got the 'You already have this unique item' message.
The Bracer vanished, fortunately I found it again in another bank slot.
The rest of my bank wasn't so fortunate, I lost between 3 to 5 bags of armor, weapons, bronto-hide and assorted collectable stuff.