Why does background image disappear, UNCHECKED - when the 3d view is closed, re-opened, or duplicated? I open a blank project, add a background image, and an object.  Closed the 3d-view, opened it again and the background image was GONE.  I revert-to-saved, and image is restored.

This is NOT an ORTHO or PERSPECTIVE issue.  In my screen capture - you can CLEARLY see, on my the bottom window (which I thought was a copy of the same 3d view) - the toolbar, "BACKGROUND IMAGES" is UNCHECKED and the file does not exist.

Re-create problem:

1) open new project
2) Add background image
3) select "3d-view" from the bottom toolbar, where "timeline" defaults to.
The background image settings are saved to the 3DView that the properties region is attached to. By changing another editor to a 3DView a new set of default values are used, they don't get copied from another 3DView.

If you setup the background images and then split the 3DView, then the background settings will get copied to the new editor.