The 1.8.4 release of Doxygen generates invalid <programlisting> elements in some cases, resulting in an orphaned </link> element inside the <programlisting> node. Sample validation error output:

struct_h_i_d___unit__t.xml:5: parser error : Opening and ending tag mismatch: para line 4 and programlisting 
    <programlisting>#include <HIDParser.h></link></programlisting>

The issue appears to be at line 1174 of src/docbookgen.cpp:

    if (!nm.isEmpty())
    {
      t << "<para>" << endl;
      t << " <programlisting>#include ";
      if (ii->fileDef && !ii->fileDef->isReference()) // TODO: support external references
      {
        t << "<link linkend=\"" << ii->fileDef->getOutputFileBase() << "\">";
      }
      t << "&lt;" << nm << "&gt;" << "</link>";
      t << "</programlisting>" << endl;
      t << "</para>" << endl;
    }

The opening <link> item is conditionally generated if a file definition is present, however the closing </link> is generated under all circumstances.