Comment 3 for bug 571057

(Also, for what it's worth, the slapd.postinst script does include a package-version check which attempts to prevent the new line from being added more than once. However, since the slapd-failure prevents the package from reaching "configured" status, the script is still trying to upgrade from the older package version each time it's executed, and thus it would add a new copy of the line each time you ran "apt dist-upgrade".)