Usually I don't care about the RT CPU value, neither about the RT CPU vs FX CPU relation. As long as a project is running, it's running and if not I raise the buffer. And it's not a big issue either, but triggered by the tc electronic thread I discovered this, which I find a bit strange.

Is this a bug? The upper is a 49 track mix, the lower a single track mastering. Does anyone have an explanation for this?