Ralph, this is not a Beta10 problem. It has always been like that. It's common to some other screen savers too. - If you blank one screen out, that's what you get!... A blank screen!
I know this is not a beta 10 problem but it is the beta that introduced the 'display on monitor x" dialog... (I think).
.... Try Windowed mode with the window on the primary, then work on the secondary monitor. - That works for me.
My secondary screen is the "old" one I used to have.. it is smaller and tucked away on the corner of my desk.. Working on it would kind of negate the excuse(s) I used to justify a 22" wide screen.
Having a full screen option on the second monitor would be at least as desirable as having a window option. or panning across two monitors.. .in fact with Jim's MA3 panning across two removes "most" of the motion, I suspect those with 3 monitors loose "all" panning.. Which is a key feature of the MA3 to show off its 3D characteristics.
But... this is just my opinion and I appreciate that Jim wants to move on..