Q on incremental processing and count()

Hi people,
I'm new to this list but with some experience in Cocoon.
Now I have a probem I cann't solve myself.
I use xalan as transformer.

My xml looks like this:
<table>
 <thead>
  <th-row>...</th-row>
  <th-row>...</th-row>
 </thead>
 <tbody>
  <row>...</row>
  <row>...</row>
 </tbody>
</table>

In my xsl I need a variable which is the count of <th-row>

If I use:
<xsl:variable name="col-num">
 <xsl:value-of select="10"/>
</xsl:variable>
The I see the incremental processing works fine.

But I have to use:
<xsl:variable name="col-num">
 <xsl:value-of select="count(thead/th-row)"/>
</xsl:variable>

But now I see the result if all row nodes are processed.
I also changed to <xsl:value-of select="count(thead[position() = 1]/th-row)"/>
but also this didn't help.

Can anybody tell me the solution or is this not possible?

Regards,
Michael

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list