The following table where only the two latter of the three cells in the table header are actually marked as headings fails to export to PFD.

It might seem strange not to mark the first cell as a heading (using "||") but the rendered HTML I believe is correct and displays as desired in the browser:

<table class="wikitable">
<tr>
<td> <th>col1</th><th>col2</th></td>
</tr><tr>
<th>row1</th><td>a </td><td>b</td>
</tr><tr>
<th>row2</th><td>a </td><td> </td>
</tr><tr>
<th>row3</th><td> </td><td>b</td>
</tr><tr>
<th>row4</th><td> </td><td> </td>
</tr>
</table>

The export to PDF fails with the following error:

com.atlassian.confluence.importexport.ImportExportException: org.apache.fop.apps.FOPException: stream:41:0 A table cell must be child of fo:table-row, not fo:block at com.atlassian.confluence.importexport.impl.PdfExporter.generatePDF(PdfExporter.java:161) at com.atlassian.confluence.importexport.impl.PdfExporter.doExportEntity(PdfExporter.java:137) at com.atlassian.confluence.importexport.impl.AbstractRendererExporterImpl.exportPage(AbstractRendererExporterImpl.java:119) at com.atlassian.confluence.importexport.impl.AbstractRendererExporterImpl.doExport(AbstractRendererExporterImpl.java:85) at com.atlassian.confluence.importexport.impl.PdfExporter.doExport(PdfExporter.java:80)