reason you are having that problem is because there are 2 bank window files, one is for the new 24 slot bank and one is for the old 16 slot bank, in your UI folder. these windows are called EQUI_BigBankWnd and EQUI_BankWnd
EQUI_BankWnd = 16 slot window
EQUI_BigBankWnd = 24 slot window
the old default UI had both of those in it, however...
EQUI_BankWnd = was 8 slots
EQUI_BigBankWnd = was 16 slots
as you do not have the new PoR expansion, the game will no longer allow you to use the Big window, it is set to load up the smaller one, which is why you are seeing an 8 slot window. in order to fix this you will need to open up the NEW default folder, copy its EQUI_BankWnd (which is now a 16 slot bank in that folder) and paste it into your Default_Old UI folder. Problem should then be solved =)
