Odd.
I was checking an epub a few days ago, and ADE did honor a page-break-before, but now I need a sanity check. I can't double-check till I get home, but my curiosity bump is itching furiously.
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I was able to get ADE working from my portable drive.
Divs with Page-break-after are indeed working. This is V 1.8 on XP Pro SP3.
I don't know that top-margin displays are "pixel-perfect", but it definitely shows a difference between small and large margin settings.
Weird.