I've done some playing around and (tried to) remove various things, and still have not solved the "jumping" issue. But I became curious about the graphics being exported after Acorn pointed out the file size of some of the exported graphics. So I did a quick test. I created a brand new page (new file), with the default page size of 760 x 1000 (SVGA). I colored the page background cyan, left the pasteboard alone, and placed a single large black circle in the middle of the page. I then exported it. Here is what I saw:
0.gif - appears to be a single, transparent 1x1 pixel image (1k)
2.png - a large cyan rectangle, 774 x 1014 pixels (5k)
4.png - a large black circle (3k)
4@2x.png - a second copy of the large black circle (6k)

The option was not available to tile the page background making it a 1x1 pixel graphics as Egg mentioned.
Is this expected behavior? I only ask because Egg mentioned tall, thin filled rectangles as a potential cause for my site's "jumping" problem.