HTTrack resumes interrupted downloads.

What is the complete command (incl. all options set) you are using?
Also, does the website make use of "statically" named resources, or does it
make use of "dynamic" parts, which change each time even for the one and the
same page? 

There can be multiple reasons for your situation, but which needs
clarification in some details first before a conclusion can be drawn that
httrack has an error.