Comment 10 for bug 457702

There's another call to "reboot": after logout from your Gnome session ldm checks whether there's a new version of the NBD image on the server. If there is, then a reboot is issued.
In the source of the "ldm" package this is in the file "rc.d/I01-nbd-checkupdate" at the very end of the script.

The package available at https://launchpad.net/~opinsys/+archive/ppa/+sourcepub/836591/+listing-archive-extra does not yet include the fix for the above problem (it contains the fix only for the regular reboots through the GUI), but the trunk version of the ldm package (available at http://bazaar.launchpad.net/~ltsp-upstream/ltsp/ldm-trunk) already has this fix, so probably the next release version of ldm will contain it too.