The problem didn't occur in XL2007 under the same setting circumstances--another part of the mystery is in custom footer I inputted stuff* to make it label the pages 1 of 200, 2 of 200, etc..., but even though I selected enough rows for two pages the print prieview shows 1 of 1 with the bottom margin blown out as described. Most annoying.
*PAGE &[PAGES] OF &[PAGES]
Again, when Print Active Sheets is selected under Settings, the margins as is work as they should...even when I scroll down to to where the two pages work of lines are. It's only when I have Print Selection selected for highlighted cells that the bottom margin is disrespected by XL10.
I appreciate your attempt to help though, thanks Andrew.