webmail not working (on 20.09)

I don't know whether it's a reqression for newer versions (I'm a new user), but when I try to set up a very basic mail config, I get the following error:

error: The option `nixcloud.webservices.roundcube.mail.mydomain.me.meta.description' defined in `/nix/store/5pikrdbaqj8jszb1dwj723b61mw29zj3-source/modules/web/services/roundcube' does not exist.

where mydomain.me is the domain defined under nixcloud.email.domains = [ "mydomain.me" ];

The only way I found to get rid of this error is to disable webmail with nixcloud.email.webmail.enable = false; (all of which is undocumented BTW).