I looked into this myself. and I also got 2 duplicates of the shared chest.
After much vexation, I have come to the conclusion that LokaID's need to be made for the additional tabs.
Tab1 - LokaID="UI_SHAREDCHEST" (we got this one already)
Tab2 - LokaID="UI_SHAREDCHEST2"
Tab3 - LokaID="UI_SHAREDCHEST3"
I'll keep digging to see if I can find where the UI definitions are handled and see if I can create the additional chest tabs.
If I can find the UI definitions, I think I'll try for 2 player chests and 2-3 shared. (Yes, I collect that much crap. )
Could u explain how to do this? Please