On a 10.6.8, six core intel Xeon, I just upgraded Nisus from the latest NP 1.3 to NP 1.4.2 and a 101 page document 10pt Times Regular reflowed down to 100 pages. For this particular document, an early stage MS, the reflow doesn't matter. But if anyone has a document where a reflow would matter, it might be as well to check whether anything shifted when upgrading.
Regards
AlanD