Rules on bottom of some tables show up on screen but not in PDF...?

This is baffling me. I have several tables in the book I'm working on, and most of them are fine. There are, however, a handful which either had no outer "bottom" rule  at all, or it was present when viewing the FM file, but saving, printing, or publishing as PDF results in those rules disappearing. I used Custom Cell Ruling and Applied Ruling style "From Table" and the frame rule appeared on screen, but still won't show up in the print PDF. Any ideas?