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.
What formatting engine are you using?
We print to PDF in Arbortext 7.1 (File > Publish > PDF File).
If this was a FOSI stylesheet, I could help, but you have XSL stylesheets.
We have a FOSI stylesheet that was provided by a conversion vendor (40051C_6_0.fos). This file is available at this site: https://pubsweb.redstone.army.mil/DTD-FOSI/Webpages-60/ALLDTDs-AMCOM.html.
I should have mentioned earlier that the Arbortext files were converted from Microsoft Word and we're now doing cleanup.
The FOSI is only for the Edit window display. XSL is provided for print/PDF output.
You should also have a set of .XSL files for composition. If not then check with the army or your supplier for the style sheets. Load them into your doctypes directory. We do not use 6.0, latest for us is 5.0, but there should be a xsl named something like xslfo-main-v6.0.xsl or something like that. Try composing using this one or something close. It uses the xsl engine in publisher. Good luck.