Using the standard autoidx.xsl, if you have a seealso, you should see something like the following:
primary
See also term
secondary, 12, 34
However, instead, there is a comma after the primary term (in this case it would be: "primary,"). There should only be a comma if there are page numbers for the primary term alone.
The problem occurs on line 317 in the file autoidx.xsl, in this template: <xsl:template match="d:indexterm" mode="index-primary"></xsl:template>
The line reads:
<xsl:if test="$refs<span>[not(d:see) and not(d:secondary)]</span>"></xsl:if>
But it should be:
<xsl:if test="$refs<span>[not(d:see) and not(d:seealso) and not(d:secondary)]</span>"></xsl:if>
The version of autoidx.xsl is the current top of tree (9856).