If you use the option '--do-not-recatch' to avoid redownloading files that have
been reased on the local hard disk, the first update of the mirror (with
parameters '-iC2%n' ) works as expected. On subsequent updates, though, erased
files (those that the first update correctly omitted) are redownloaded. Am I
doing something wrong? 

One thing I noticed is that, after the first update, the 'new.*' cache files
are noticeably smaller than the 'old.*' ones. If I have understood correctly a
previous post 
(http://forum.httrack.com/readmsg/9799/9784/index.html), looks like the
problem is due to httrack caching (in the 'new.zip' file) only the files that
are still in the local mirror; so when doing a further update, it thinks the
locally erased files are new ones. 

I'm using httrack v3.40; don't know if this applies also to previous
versions...