Strange desktop behavior on my Xubuntu 16.04 laptop

[MR ZenWiz]

I have an HP 8710w laptop that I use most often on weekends or when
I'm visiting friends.

Starting a couple of days ago, the following strange behavior began to
manifest on it.

1. The right mouse button has no effect on the open desktop screen
space.  It's supposed to bring up a menu and it doesn't.  The button
works fine inside any open window, just not on the desktop.

2. The desktop is supposed to be a dark green, but as soon as any
window is opened, or even the panels, the background where the
window/panel is goes to the ubuntu default background minus the mouse
image.

3. If I try to change the desktop settings with the settings manager,
they don't take.  In fact nothing happens at all.  It''s as if there
is no desktop manager.

I'm running lightdm version 1.18.3 if that matters.  It's unchanged
from the install.

I just ran a full update and rebooted, and it is still happening.