Alfred, thanks for your message. After looking at my gedcom in a text editor I have found that in order for the source info to be included in my PAF export, I have to check "include notes" as well as "include sources." If I check "include sources" but not "include notes," the sources don't appear in the gedcom data. Unfortunately, for this particular purpose I do not want to include notes.
Apparently what happens is that the NOTE tag is being attached not only to the info I enter in the regular notes screen, but also to any comments or page numbers I include with individual citations. This affects probably 99% of my citations. Any ideas how to differentiate between these two types of notes when exporting? Or am I doing something wrong with my data entry? (I hope that's not the case, because I have 8,000+ records that I really don't want to have to reenter!!)