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.
1) open new project 2) Add background image 3) select "3d-view" from the bottom toolbar, where "timeline" defaults to.