[...]
One of the simple tasks that I have never succeeded in getting Cupsys to
do, even after many hours of fiddling, was to describe the same
printer hardware in two ways, one simplex and one duplex.
[...]
Try the experiment you described: install Lenny from netinst, install
python2.5, then remove cupsys. If the problem recurs, then you might
have found a bug.
I already did exactly that, except that I also installed cvs, emacs,
and ssh-server, too, and I don't believe that those packages are
implicated. Therefore, I think I've found the bug already. And I
have a workaround: just remove cupsys first of all, *before*
installing python-2.5.