This change in nUI_BagBar.lua fixes the problem and should *not tested yet* work in 4.1 as well.
PHP Code:
if _G["KeyRingButton"] then
nUI_BagBar.Buttons[1] = _G["KeyRingButton"];
nUI_BagBar.Buttons[2] = nUI_ButtonBagButton;
nUI_BagBar.Buttons[3] = _G["CharacterBag3Slot"];
nUI_BagBar.Buttons[4] = _G["CharacterBag2Slot"];
nUI_BagBar.Buttons[5] = _G["CharacterBag1Slot"];
nUI_BagBar.Buttons[6] = _G["CharacterBag0Slot"];
nUI_BagBar.Buttons[7] = _G["MainMenuBarBackpackButton"];
else
nUI_BagBar.Buttons[1] = nUI_ButtonBagButton;
nUI_BagBar.Buttons[2] = _G["CharacterBag3Slot"];
nUI_BagBar.Buttons[3] = _G["CharacterBag2Slot"];
nUI_BagBar.Buttons[4] = _G["CharacterBag1Slot"];
nUI_BagBar.Buttons[5] = _G["CharacterBag0Slot"];
nUI_BagBar.Buttons[6] = _G["MainMenuBarBackpackButton"];
end