Odd Aperture behaviour of Secondary Monitor.

According to Apple:

Alternate: Displays the currently selected photo in the Secondary Viewer. The Secondary Viewer shows only one photo, even when you have the Main Viewer set to display multiple photos.

Not on my computer.

Span: Splits the display of the currently selected photos between the Main Viewer and the Secondary Viewer. For example, if you select seven photos to view, the Main Viewer shows as many as fit its screen size, and the remaining photos appear in the Secondary Viewer. Thus, one Viewer might show four photos, and the other Viewer might show the remaining three of the seven. Span is also used if you want to compare photos and show one photo per display.

Not on my computer.

Viewers
  Main viewer = Multiple
  Secondary viewer  = Span.
  Mode = browser.

Select one or more images in browser, whatever number I select is shown on secondary monitor.

  Change mode to filmstrip.

None selected:  Both image viewers are blank.
One selected:  Two copies of same image.
Two selected:  Both screens show image #1.  Neither shows Image #2
Three Selected:  Both screens show images #1 and #2, neither shows #3
Four selected:   Both screens show images #1 and #2, neither shows #3 or 4
Five selected:  Both screens show images #1, #2 and #3, neither shows #4 or  #5
Six selected:  No change from #5 #6 not shown ether
Seven selected: #1-4 show on both #5-7 show on neither.

Change mode back to Viewer.  I now have two screens of 4 images. Same 4 on both.

Viewers
  Main viewer = Multiple
  Secondary viewer  = Alternate.
  Mode = browser.

Behaves exactly the same as in Span.  Select 4 in browser – they show as selected in browser, and all 4 show up in secondary.

Change to viewer.  Main  and second both show all the images I had selected at the time.  If I manually deselect, I end up with one image on both the Main and Secondary.  Both viewer and secondary respond to middle mouse button roll in changing the primary (heavy outline) image.

Change to filmstrip:  Whatever I have selected on the strip shows up in both the viewer and the secondary.

Viewers
  Main viewer = Multiple
  Secondary viewer  = Mirror.
  Mode = all.

Behaves exactly like Alternate does.