[docbook-apps] colspan support for table/informaltable

I'm not sure if I'm completely missing the mark.

Does Docbook not handle colspan for informal tables?

This source:

<informaltable border="1" >
	<tbody>
		<tr>
			<th colspan="4">Lorem Ipsum</th>
		</tr>
		<tr>
			<td>Fie</td>
			<td>Fi</td>
			<td>Fo</td>
			<td>Fum</td>
		</tr>					
	</tbody>				
</informaltable>


Results in:
  - - - - - - -
|Lorem Ipsum  |
  - - - - - - - - - - - - - - -
|Fie          | Fi | Fo | Fum |
  - - - - - - - - - - - - - - -

No "number-rows-spanned" attribute is applied to the final FO.

I'm Using:

docbook-xsl-1.74.3/fo
Saxon 9.1
Antenna House 4.3


Thanks!

~Shane Handford