I launched httrack two times:

httrack <http://www.example.com/foo/bar.html> -
O /path/to/mirrordir,/path/to/cachedir
httrack 
<http://smith:mypassword@www.example.com/protected/bar.html> -
O /path/to/mirrordir,/path/to/cachedir

The result: only the files of the second download are found.
Should I should specify a separate cachedir for each 
download?