[spiel2001]

Okay... I found the problem and it's an easy fix for those who don't want to wait for the update Sunday night.

Edit [ Interface > AddOns > nUI > Bars > nUI_BagBar.lua ] and go to line 193 where you'll see this code block...

        -- set the appropriate bag bar visibility
        
        if nUI_Options.bagbar == "off" then
            frame:SetAlpha( 0 );
            frame.alpha = 0;
        elseif nUI_Options.bagbar ~= "mouseover" then
            frame:SetAlpha( 1 );
            frame.alpha = 1;
            nUI_BagBar:SetScript( "OnUpdate", onBagBarUpdate );
        end 

... and add an "else" statement to it so it looks like this...

        -- set the appropriate bag bar visibility
        
        if nUI_Options.bagbar == "off" then
            frame:SetAlpha( 0 );
            frame.alpha = 0;
        elseif nUI_Options.bagbar ~= "mouseover" then
            frame:SetAlpha( 1 );
            frame.alpha = 1;
        else
            nUI_BagBar:SetScript( "OnUpdate", onBagBarUpdate );
        end

That should do the trick.