If I try to change ISO from AUTO to "ISO 100" in the "ISO Setting/NR" menu and press "OK", it changes to "ISO 320" only! Anyone else have this problem?
It's most probably not a bug but feature This could happen in case of enabled Dynamic Range Compensation (at Auto or Strong level). A similar thing happens if you use Continuous mode and AutoISO, where the lowest ISO value the camera picks is 400. Hope this helps?
OK too late I was interrupted during writing my answer. This behavior may not look intuitive, but at least it's described in help.