Looking further, at System-Admin-Update Manager, I see "Other updates (LP-PPA-bryceharrington-purple)" are available.
Two updates were shown, xserver-common (Size 80 KB) and xserver-xorg-core (Size 2.0 MB) so I applied them and rebooted, and so far it appears to have eliminated the problem of crashing to the login screen. The other anomalies are minor and cosmetic so I'll live with them.
Looking further, at System-Admin-Update Manager, I see "Other updates (LP-PPA- bryceharrington -purple) " are available.
Two updates were shown, xserver-common (Size 80 KB) and xserver-xorg-core (Size 2.0 MB) so I applied them and rebooted, and so far it appears to have eliminated the problem of crashing to the login screen. The other anomalies are minor and cosmetic so I'll live with them.