What I am finding is it doesn't matter how many tabs you have. It actually has do to with how many pieces you have combined in the Bank / Inventory UI.
You cant have all the slots in both UI's using 46 pieces per bag. I had to cut back some bags to less pieces shown. If I didn't when I open up bags, I couldn't see anything.
Pieces: (not counting any other then bags)
1380 Pieces for bank (30 bags at 46 slots)
460 pieces for Inventory (10 bags at 46 slots)
<Pieces>IW_Bag1_Slot1</Pieces>
<Pieces>IW_Bag1_Slot2</Pieces>
<Pieces>IW_Bag1_Slot3</Pieces>
<Pieces>IW_Bag1_Slot4</Pieces>
<Pieces>IW_Bag1_Slot5</Pieces>
<Pieces>IW_Bag1_Slot6</Pieces>
<Pieces>IW_Bag1_Slot7</Pieces>
<Pieces>IW_Bag1_Slot8</Pieces>
Etc.....