Delegate=0 vs ipv6=0?

I found a strange luci thing today.

If I in luci and a interface on 19.07.7, 19.07-snapshot and 21.02-rc1 turn off the ’Use builtin IPv6-management’ checkbox. Then Luci writes delegate=0 to the network interface config.

But if I do the same in the master snapshot with Luci. Then Luci writes Ipv6=0 to network config file.
I cant even find a delegate setting as of today?
But it should actually write ipv6=0 since OpenWRT14 if Barrier Breaker is OpenWRT version 14?