said Slávek Banko:
| > Another, weirder issue: after the upgrade and a reboot, the machine | > goes to GDM instead of TWM, which worked just fine before the upgrade. | | Yes, for some reason not yet known, it may happen that during the | upgrade it may switch to another DM if another DM is installed. | | You can use dpkg-reconfigure tdm-trinity to switch back. Or uninstall | another DM if not needed.
Thanks again. That's what I did; mostly wanted to kind of report it in case a.) it's a strange bug or b.) I had broken something else! (And as always, the TWM/TDM confusion is mine.)