Now, I'm no expert...but the fold should be on the left then on the right if you scan every page. For pages 29-31 in the scan the fold (and staple holes) are all on the left. And they are on the right in 28 and 32. For pages 19-21 you can't see the fold or staples, but you can see a fold line in the upper left corner. It too should flip from left to right and back...and it is on the right on 18 and 22.
So I'm pretty sure it is scanner's error.