Hi Marcus,
Thanks for the follow-up! Yes, I have an .htaccess in place (a fairly complex one) and it has been running without problems or changes for at least several months. In fact, the core rewrites have not change for over a year. That is not to say it isn’t the problem, it just isn’t one of the variables that changed. The difficulty started when I upgraded my EE+MSM installation to the latest 2.2.0 from 2.1.4 beta (I skipped over 2.1.5 beta).
Deleting the contents of the .htaccess file had no effect on the issue. Neither did setting “RewriteEngine off”.
My sites are hosted on EngineHosting so I suspect the problem would be more widespread if it were purely a hosting issue. That being said, PATH_INFO did NOT appear as one of the supported server variables in phpinfo.