Problem with msxsl:node-set

I have this variable, whose internal workings aren't very important:

        <xsl:variable name="uniqueClassDates">
                <xsl:for-each
select="ArrayOfAttendance/Attendance/ClassDate[number(substring(.,1,4)) &gt;
0001
                and not(. = preceding::ClassDate)]">
                        <xsl:element name="date">
                                <xsl:value-of select="."/>
                        </xsl:element>
                </xsl:for-each>
        </xsl:variable>

Which holds this value:

<date>2004-01-10T00:00:00.0000000-05:00</date>
<date>2004-01-11T00:00:00.0000000-05:00</date>
<date>2004-01-12T00:00:00.0000000-05:00</date>

The problem occurs while I am running this comparison:

<xsl:if test="msxsl:node-set($uniqueClassDates)/date[$begin] = ClassDate">

In this case, $begin will be 1, 2 or 3.  However, if I pass ClassDate with
any value that is contained in $uniqueClassDates, it always returns true.
How can I limit the logic to only return true when the $begin position of
date matches ClassDate?

Here is entire template:


<xsl:template name="indexAttendanceCells">
                <xsl:param name="begin"/>
                <xsl:param name="end"/>
                <xsl:choose>
                        <xsl:when test="$begin &gt; $end"></xsl:when>
                        <xsl:otherwise>
                                <xsl:variable name="attended">
                                        <xsl:if
test="msxsl:node-set($uniqueClassDates)/date[$begin] = ClassDate">
                                                <xsl:text>true</xsl:text>
                                        </xsl:if>
                                </xsl:variable>
                                <xsl:choose>
                                        <xsl:when test="$attended = 'true'">
                                                <td>
                                                        X
                                                </td>
                                        </xsl:when>
                                        <xsl:otherwise>
                                                <td>
                                                        &#xA0;
                                                </td>
                                                <xsl:call-template
name="indexAttendanceCells">
                                                        <xsl:with-param
name="begin" select="$begin + 1"/>
                                                        <xsl:with-param
name="end" select="$end"/>
                                                </xsl:call-template>
                                        </xsl:otherwise>
                                </xsl:choose>
                        </xsl:otherwise>
                </xsl:choose>
        </xsl:template>