After further experimentation, starting setup from XTerm using: sudo /usr/bin/mythtv-setup successfully starts the GUI. The notice that the backend processes must be closed appears, but no password request dialog is displayed. I hope this helps to identify the problem.
After further experimentation, starting setup from XTerm using: sudo /usr/bin/ mythtv- setup successfully starts the GUI. The notice that the backend processes must be closed appears, but no password request dialog is displayed. I hope this helps to identify the problem.