avoid errormessage on zone transfer?

Hello once again,

to fetch the root zone we use a config template common an all hosts.

     zone:
         name: "."
         zonefile: "data/root"
         request-xfr: 2001:500:2f::f NOKEY  # f.root-servers.net
         request-xfr: 192.5.5.241 NOKEY     # f.root-servers.net
         ...

An IPv4 only host still try to connect to the first address which  
obviously fail:

     error: xfrd: 2001:500:2f::f cannot create tcp socket: Address  
family not supported by protocol

I tried to add "do-ip6: no" and even add an "outgoing-interface: "  
statement to the zone block.
That does not circumvent the error message that trigger an alarm in  
our monitoring system.

Any chance to force ipv4 only? I suspect "do-ip6: no" should do the  
job but unfortunately it doesn't.

Andreas