Slowness on local install, just with some URLs

Hi, I'm having a weird issue with my local installations of the 1.3
validator.

I'm validating this URL:

http://www.jedermann-gruppe.de/cms/der-verein

If I validate it on http://validator.w3.org it just takes 2 seconds to
respond, but when I do it on my local installation, it takes about a minute.

Other URLs are fine, but all within this site are super slow. It does not
seem a connectivity issue, as I can browse this site fine, ping, etc.

It does not happen on my local installation of validator.nu.

I've tried on 3 different servers, with ubuntu 32 bits and 64 bits, and
different locations (a dedicated server and a pair of virtual boxes on my
machine).

I can't find any error on the Apache logs, is there any other log to check?
Please notice that the validation goes OK, it returns 7 HTML errors, it's
just slow.

Can anyone with a local installation of the validator verify this?

How can I investigate / solve this?

Thanks!

Jaime