> somehow httrack doesn't work correctly. 
It's working correctly.

> I need to portion the download process (cancel it
> and continue the interrupted download the following
> time).
When you cancel it, previously downloaded html and related files are not part
of the current mirror. Httrack then deletes them (options -> Build -> Do not
purge=unchecked)
In addition anything not downloaded is gone from the cache, so the next time,
they will have to be redownloaded.

> So what's wrong with httrack?Nothing. It's doing exactly what you told it to
do.

Stop canceling it. Just Mirror -> Pause.