You (and Brian) are right on the fact that base ISO can be changes on a fly and the metering system will control ISO from that starting point and up to the Max value set in Auto ISO menu.
I was referring to a situation when Nikon allow to override base ISO above the max value, giving false sense of "security" but image will be recorded at ISO max value from the Auto ISO menu and thus expected shutter speed/Aperture will not be used. Photographer has to go into the menu and either disable auto ISO or increase max value in the menu.
I personally prefer to use the same logic for ISO override, as let’s say it used with FV value lock – it locked until metering system is off. I do not keep my auto ISO to all available range – I usually cap it to 800, 1600 and sometimes to 3200. But there is always possibility that I need a shot at ISO 6400 and to get it I need to go to the menu and turn off Auto ISO.
It very easy to implement with FW update not to allow ISO to be increased on display above the value set in max auto ISO menu is this feature is up. Photographer would right away know if ISO on LCD doesn’t clime past 1600 – that is the limit set auto iSO menu.
But it’s also easy to implement to allow manual override passed max value until camera is off or even metering system is off.
Just my 2 c.
Best regards, Vlad
P.S. not related to this discussion - one of the reason I’ll upgrade D7000 to D600 because on D7000 in LV mode mirror is going up for the metering before taking a shot - this IS THE BIGEST drawback of D7000 for me. I leaned to deal with D7000 and love this camera, but “LiveView” implementation is not really that good (like changing aperture is not changing LCD image brightness ( I bet that can be fixed in FW release, 1/30s the lowest auto shutter speed and mirror slam things (last two are hardware limitations, I’m sure) that I’m really unhappy with...