I get this all the time when I scan bills at home. The initial scan goes through and it shows me three or four different scannable sections on one page. I might scan the same page again, and the whole page is treated as one section (no divides). There's no real rhyme or reason except that the scanner thinks there is more than one document on the unit.
I don’t have Photoshop Elements on my current PC, but I have Photoshop CS2 which I use professionally (and have been for a long time..Photoshop’s up to CS4 now). CS2 doesn’t even include Divide Scanned Photos, I had to install it at home to see what was actually happening :)