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not your regular ipv4/ipv6 dns issue

Hi all,
We are seeing strange delays in dns resolving with apt-get and wget. Tried various public dns servers (for example google dns, opendns) I used tcpdump to see what actually happens, and we found out that apt-get makes two requests for security.debian.org: 
standard query A
and
standard query AAAA
But only the first query is answered...
Five seconds later, apt-get asks the same AGAIN, but this time waits for an answer, and obtains both A and AAAA addresses: 
No.     Time        Source                Destination           Protocol Info
      1 0.000000    192.87.143.xx         8.8.8.8               DNS      Standard query A security.debian.org
      2 0.000018    192.87.143.xx         8.8.8.8               DNS      Standard query AAAA security.debian.org
      3 0.025487    8.8.8.8               192.87.143.xx         DNS      Standard query response A 212.211.132.250 A 212.211.132.32 A 195.20.242.89
      4 5.004465    192.87.143.xx         8.8.8.8               DNS      Standard query A security.debian.org
      5 5.005530    8.8.8.8               192.87.143.xx         DNS      Standard query response A 212.211.132.250 A 212.211.132.32 A 195.20.242.89
      6 5.005601    192.87.143.xx         8.8.8.8.              DNS      Standard query AAAA security.debian.org
      7 5.030211    8.8.8.8               192.87.143.xx         DNS      Standard query response AAAA 2001:8d8:580:400:6564:a62:0:2 AAAA 2001:a78:5:1:216:35ff:fe7f:6ceb AAAA 2001:a78:5:0:216:35ff:fe7f:be4f
Note: of course security.debian.org has an AAAA record, and my machine is also 100% ipv6 enabled. (and generally ipv4/ipv6 both work as expected) 

We see no delays at all when using 'host' to get the info:


host ftp.nluug.nl
ftp.nluug.nl has address 192.87.102.42
ftp.nluug.nl has address 192.87.102.43
ftp.nluug.nl has IPv6 address 2001:610:1:80aa:192:87:102:43
ftp.nluug.nl has IPv6 address 2001:610:1:80aa:192:87:102:42
root@ws063:~#


If we use 'wget' to download files, we see the same behaviour:


wget http://ftp.nluug.nl/README.nluug
--2013-11-06 13:55:54--  http://ftp.nluug.nl/README.nluug
Resolving ftp.nluug.nl (ftp.nluug.nl)... 192.87.102.43, 192.87.102.42, 2001:610:1:80aa:192:87:102:42, ...
Just the resolving takes 5 seconds, but the result is good: both ipv4 and ipv6 addresses are returned. Downloading goes with normal speed. 

Interestingly: When instructing wget to use ipv4 or ipv6, BOTH work quickly.
> wget -6 http://ftp.nluug.nl/README.nluug
or
> wget -4 http://ftp.nluug.nl/README.nluug
work quick.
I have also tried setting ipv6-addresses-only in /etc/resolv.conf, with exactly the same problems/results.
Can anyone here give me soms tips or clues what could be the problem here? Really hope someone has a clue... 

Regards,
MJ
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