Honestly, I have a hard time seeing how the two could be related. Are you perhaps clearing the MEF container somewhere or neglected to make the AuthenticationService a singleton. This sounds to me that under certain circumstances you are getting a new instance of the AuthenticationService for some reason, which is then logged out by default.
I would suggest you remove your application from the equation and put together a little sample app to see if you can reproduce the issue. FWIW, you can try TempHire, too, it allows hitting enter in the search box and most of the dialogs. None of these actions are causing the AuthenticationService to log out.