"freebsd-update -r" and IPv6

[Victor Sudakov]

Dear Colleagues,

I have an IPv6-only host for test purposes. I have noticed that I can
never successfully complete "freebsd-update -r 11.2-RELEASE upgrade"
procedure on this host, it always complains about 

Fetching metadata signature for 10.4-RELEASE from update5.freebsd.org... failed.
No mirrors remaining, giving up.

The name of the update server can be different each time, like
"update4.freebsd.org", "update5.freebsd.org" etc with the same result.

Is this supposed to work? Are all the servers necessary for
freebsd-update operation available via IPv6?

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
AS43859