BRIGHTSCRIPT: ERROR: roSGNode.ObserveField: no active host node

I'm in the process of implementing Roku Voice support.  For the most part, I have it working except for one issue.  The ObserveField events do not fire on my Video screen.  It's somehow related to the way I start the video content.  

During normal processing, the video content is started from a Details screen, and the events fire as expected.  My (new) Voice code starts the Video screen from within main.brs in the message loop.  I detect the "transport" event and show my Video screen.  The video starts and responds to voice commands.

If I use the remote to stop the video and return to the top scene (Grid screen), the events do not fire because when the Video screen was started, I get:

BRIGHTSCRIPT: ERROR: roSGNode.ObserveField: no active host node

on some field values I track to know when the Video state has changed.

Can anyone shed some light on how to resolve this?