This doesn't seem all that easy to reproduce (i. e. getting into the state where /etc/X11/default-display-manager says just "lightdm")? Anyway, this is primarily an upgrade issue and does not affect a clean install, so it can be fixed in an SRU.
This doesn't seem all that easy to reproduce (i. e. getting into the state where /etc/X11/ default- display- manager says just "lightdm")? Anyway, this is primarily an upgrade issue and does not affect a clean install, so it can be fixed in an SRU.