Nested for-each-group

Hi all,

Given this xml:

<tgroup>
	<col colname="C.HPC" width="17"/>
	<col colname="C.HPB" width="23"/>
	<col colname="C.HPA" width="29"/>
	<col colname="C.I0F" width="17"/>
	<col colname="C.I0E" width="14"/>
	<spanspec namest="C.HPC" nameend="C.I0F"/>
	<spanspec namest="C.HPC" nameend="C.I0E"/>
</tgroup>

I'm trying to sum the colwidths specified by the spanspecs.  I used to
use a recursive template, which I'm trying to replace using a nested
for-each-group:

<xsl:template match="spanspec">
    <xsl:variable name="namest" select="@namest"/>
    <xsl:variable name="nameend" select="@nameend"/>

    <xsl:for-each-group select="preceding-sibling::col"
group-starting-with="*[@colname = $namest]">
        <xsl:for-each-group select="current-group()"
group-ending-with="*[@colname = $nameend]">
      		<div><xsl:value-of
select="sum(current-group()/@width)"/></div>
      	</xsl:for-each-group>
    </xsl:for-each-group>

</xsl:template>

However, this produces:

	<div>86</div><div>14</div>
	<div>100</div>

I don't understand why I'm getting the "<div>14</div>" output?  I know
it's part of the outer group, but it shouldn't be part of the inner
group.  Any ideas why its there?

cheers
andrew