In the second link, someone told that the problem may solved in the
kernel 2.6.30.
I tried to upgrade to the latest kernel via:
deb http://ftp.de.debian.org/debian-archive/debian/ lenny main
deb-src http://ftp.de.debian.org/debian-archive/debian/ lenny main
and
aptitude update
aptitude safe-upgrade
but I had no luck, nothing to upgrade.
No, of couse, because as it happens with any "stable" release, Lenny did
not provide a kernel upgrade (other than patches) from their usual repo.
I don't recall what was the last backported kernel available for Lenny
but this would be the easier solution.