I thought to report an error while facing it. I tried to create an iocage jail (backuppc) and was modifying the network options. I didn't need ipv6, so I selected Disable for ipv6 dropdown in network options. After trying to start the jail, I get:
"[EFAULT] Exception: RuntimeError:*** disable is not a valid value for ip6. Value must be new or inherit or none *** occured, destroyed backuppc."
As it's not allowed value, it might be better removed from the dropdown, and perhaps none to replace it?
While at it, please fix the help tooltip, it talks about ipv4 instead of ipv6.
This is FreeNAS-11.2-U5.