To be a little more precise:

It is not an obscure bug, these problems are repeatedly reported since years.

Look at 
<http://forum.httrack.com/readmsg/20492/20479/index.html>
<http://forum.httrack.com/readmsg/11007/10746/index.html>

Seems this is related:
<http://forum.httrack.com/readmsg/8655/8631/index.html>

Somewhere in the forum someone even supplied log and debug files and partially
worked out what happens.

Regarding misconfigured servers: Server settings (usually) are out my control.
If my browser can download things httrack should also do.

BTW: In my testing case, it is my own server running on a VM (Debian apache2
out of the box).

Program version 3.32 works and 3.33 does not. This looks like a typical
regression.

A download with ~15% files "corrupted" is a severe program malfunction.