We have attempted to replicate the issue you described but were unable to identify it. After you disable the setting, please refresh the page and observe again to see if the change takes effect.
After another power-cycle there is no longer an IPV6 address although I'm not sure the Network Status display is helpful. I think we can consider this closed now.
F2-425 Plus, 16GB RAM, 2 x 500GB WD SN700 EXT4 RAID1, 2 x 18TB WD Red Pro EXT4 RAID1, TOS 7.0.<latest>