Comment 164 for bug 417757

From libc.NEWS file:
  Starting with version 2.9-8, unified IPv4/IPv6 lookup have been enabled
  in the glibc's resolver. This is faster, fixes numerous of bugs, but is
  problematic on some broken DNS servers and/or wrongly configured
  firewalls.

  If such a DNS server is detected, the resolver switches (permanently
  for that process) to a mode where the second request is sent only when
  the first answer has been received. This means the first request will
  be timeout, but subsequent requests should be fast again. This
  behaviour can be enabled permanently by adding 'options single-request'
  to /etc/resolv.conf.

Could you try adding 'options single-request' in /etc/resolv.conf ?