This isn't a problem in NetworkManager. I finally found the right bug that describes the behavior *and* which offers a viable work-around. See https://bugs.launchpad.net/ubuntu/+source/xfce4-panel/+bug/139424 (Bug #139424).
The issue is that icon scaling in the System Tray doesn't work well if the Panel is vertical instead of horizontal. The icons can be brought back by moving the panel to the top or bottom of the screen and then moving it back to vertical.
This isn't a problem in NetworkManager. I finally found the right bug that describes the behavior *and* which offers a viable work-around. See https:/ /bugs.launchpad .net/ubuntu/ +source/ xfce4-panel/ +bug/139424 (Bug #139424).
The issue is that icon scaling in the System Tray doesn't work well if the Panel is vertical instead of horizontal. The icons can be brought back by moving the panel to the top or bottom of the screen and then moving it back to vertical.