Domain mapping issues preventing login when not set to mapped domain, any ideas?

When setting Domain mapping Configuration > Administration mapping and Login mapping to anything other than mapped domain , such as original domain, we are unable to log in. The log in screen simply stays on the login screen and does not allow one past this page. The username and password being entered is correct because entering the wrong creds generate the standard error otherwise there is no error message just the same login screen. We can however log in to the main site on all networks just not the sub domain sites. What is the underlying issue here?
All of our WPMU sites using domain mapping and multidomains are having the same issues. For now we'll leave them set to mapped domain. We're using current version of WP on some networks and 352 on others... WPMUdev plugins are current on sites running latest version of WP. Others running 352 are using plugin versions just before current. I hope this helps and provides enough info to find a solution. We would really like to use the original domain setting to better brand our network domains. Thanks!