[7.1.2] Cannot select subnet mask outside of /25-/30 when configuring IPv4 custom network on br0.XX (aka VLAN) in Docker.

As the summary says, trying to configure a custom IPv4 network on interface br0.XX (VLAN XX) in docker.

The drop down menu for subnet mask display /25 up to /30 with no option to select /8 for example.

My VLAN 20 network is a 10.0.0.0/8 as per RFC-1918.

The DHCP pool drop down allows /16 and up to /30 which doesn't make sense.