Line spacing for fonts of 16 point or more

Version: 2008
Operating System: Mac OS X 10.4 (Tiger)
Processor: Power PC

I've got a problem in both Word 2008 and 2004. When I go to print layout
view in 2008 (or page view in 2004) for a do***ent, if I've used fonts of
16 point or more, the line spacing appears double spaced. And clicking on
the toolbar icons for setting single space, space and a half, or double
space does nothing at all. At all sizes below 16, and using many fonts,
everything works fine. I first noticed this while working in Word 2008, so
I opened the do***ent in Word 2004 and have the same problem. (I am saving
the Word 2008 do***ents in compatibility mode, as .doc do***ents.)