Is there a way to disable the notification? I have noticed this from time to time on my setup as well.
I figure there has to be a way to disable messaging on a certain device.
Try going to web Admin and then to the Device Template for the Orbiter on your MD. Scroll down to near the bottom of the screen and find the 'Alert Filter Level' field. This controls what alerts are displayed by the Orbiter in the top left hand corner of the screen. By default this is set to 'All'. Try setting it to 'important' (dont use the quotes in the field of course!) or possibly 'none' (this should suppress all alerts... this might not be a good idea though). Once you have changed this field click 'Save' and then do a reload router.
All the best