Shortly, on vertical panels (doors etc...) with some concave/convex parts machine stop rotate if pad is in full contact with panel but rotate if machine is tilted little and that way pad works on its edge (not literally edge but it is not in full contact with panel, one part eg. half of the pad is in contact with panel and other half is raised). Normal for long throw Rupes or not as for example Meguiars MT300 does not rotate if the pad is not in full contact with panel which is tottaly opposite than Rupes on same panel.
Thx
Thx