Manual ipv6 cannot add prefix in gui

I was playing around with ipv6 on my 905X2, Amlogic-ng 21.1.1, I had a hard time of filling in the ipv6 parameters in the gui. For some reason the PrefixLength can’t be added in the gui ?
I finally got it working from cli with this command:
connmanctl config ethernet_xxxxxxxxxxxx_cable ipv6 manual 2001:xxxx:xxxx:xxxx::xx 64 2001:xxxx:xxxx:xxxx::1
When I look in the gui at the ipv6 setiings the PrefixLength shows @
So I think the gui field of the ipv6 prefixlength field needs some work.

The .cache/connman/ethernet_xxxxxxxxxxxx_cable/settings file now contains:
IPv6.method=manual
IPv6.privacy=disabled
IPv6.netmask_prefixlen=64
IPv6.local_address=2001:xxxx:xxxx:xxxx::xx
IPv6.gateway=2001:xxxx:xxxx:xxxx::x