olinks to chapters in same book not working

["Robert Hall" <rhall@vocera.com>]

I'm not sure whether this is a stylesheet problem or an xsltproc
problem.
Here's a quick summary:
 - DocBook 4.4, XSL Stylesheets 1.69.1
 - Modular book uses XInclude to pull in chapter files.
 - Using olinks for all cross references.
 - Using xsltproc and FOP 0.20.5 to generate FO and then PDF.
 - For each olink, xsltproc generates an opening fo:basic-link tag,
   and then, instead of closing the tag, it generates an empty one.
   When FOP encounters the empty one, it stops processing. 
   Error: internal-destination or external-destination must be specified
in basic-link

Here are the (simplified) details: