About the joystick.
I agree there is a bug/ malfunction in the way the Prophet VS joystick works. To me then the X - axis should move the joystick from A (Left) -> C (Right) and the Y - axis from D (Bottom) -> B (Top) when assigned to for example a X/Y pad like on my Novation SL MKII controller. But it does'nt do that.
The way it works now is'nt logical. It's not only moving the wrong direction when making a circle movement, it also move very "wrong" when making a pure horizontal or vertical movement. The virtuel joystick should be in the same position as the hardware, but it is'nt.
This should be fixed Arturia.
EDIT: About the random movements, then remember the movements can both be automatic and modulated. This movement perhaps also need to be checked Arturia. EDIT END
About the preset selection.
How do you select presets? How do you assign your controls - and to what?
Are you using ProgramChange, then keep in mind that ProgramChange only work with Playlists.