> If I have +*.zip in the scan rules, httrack tries to
> download external zip files

Okay, this is normal

> However, no problem when the php script redirects to the
> actual page if hide the query string is ticked, except 
with
> .tar.bz2 files :
> in any case, even with a direct link, the file is renamed
> .tar.tar

Err, probably because the server is tagging the file 
as "gzipped stream", and therefore httrack uncompress it.

You you have a live example ? I suspect the server to send 
an additional hint such as "this filename is <foo>.tar"