Rolf, Michael,
We have a 2018 build Flair, and the water still stays in the bowl. We are using the holding tank to the max, this is why I have now the Super Sense device installed, to have a better understandig of the actual filling level (and the reserve left). There is no event at all where I have the impression that the water is being sucked into the tank nor any gassing through the filled (or empty) bowl, irrespective of the filling level of the tank.
The toilet is installed with the hose connection to the tank with a "syphon" shape, the backpressure valve also present.
What is visible in the video makes me assume that there is no point of the outlet hose shaped like syphon and the backpressure valve, if given, is not really tight.
Can´t you take a picture from the backside through the maintenance opening? At least Concorde has one, not sure for Morelo.
Regards,
RAlf