Check the Windows event log (application log) and see if you see any app crashes in the Rift executable(s). That should tell you if it has detected an abnormal exit or not. If you don't see any, they either purposefully designed the client this way or there is an unplanned "normal" exit case that is a bug but doesn't process as a bug in the client's error handlers.

[edit] Also, share what platform and multiboxing software/hardware you're using when you see this as it might help the community identify where potential problems exist.