Bug#868828: www.debian.org: connection to Debian machines is very slow when IPv6 doesn't work

Package: www.debian.org
Severity: normal

Connection to Debian machines is very slow when IPv6 doesn't work.
For instance, "bts show --mbox ..." took 30 minutes.

And with reportbug,

Checking for newer versions at madison, incoming.debian.org and http://ftp-master.debian.org/new.html

also hangs for several minutes.

-- System Information:
Debian Release: buster/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 4.11.0-2-amd64 (SMP w/8 CPU cores)
Locale: LANG=POSIX, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=POSIX (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)