This option determines which settings are affected when AE & flash bracketing or AE bracketing is selected for the Auto bracketing set option in the photo shooting menu in manual exposure mode.
Flash bracketing is performed only with i-TTL or qA (auto aperture) flash control. If a setting other than Flash only is selected and the flash is not used, ISO sensitivity will be fixed at the value for the first shot when auto ISO sensitivity control is on (0 ISO Sensitivity Settings).