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="*[(_at_)colname = $namest]">
        <xsl:for-each-group select="current-group()"
group-ending-with="*[(_at_)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