No table header text in PDF

Hi,

I'm working on a document that uses the 40051 DTD.  In Arbortext, the header text for tables looks fine but when I create a PDF (File > Publish > PDF File), the table header text doesn't appear.  I tried changing the valign attribute for the header row from bottom to top and middle, but that didn't make a difference.  Also, I pasted the table code in a DITA concept topic and it published to PDF with no problem.

Thanks,

Bob