xml - ノードの最大値を取得できない

Question

属性アクションで LandLine_ExtId ベースの最大値と最小値を取得しようとしています。action value=del の Landline_ExtId の最大値が間違って返される

xml入力

<Landline_ExtId  action='add'>771534777880</Landline_ExtId>
<Landline_ExtId  action='add'>771534777881</Landline_ExtId>
<Landline_ExtId  action='add'>771534777882</Landline_ExtId>
<Landline_ExtId  action='add'>771534777883</Landline_ExtId>
<Landline_ExtId  action='add'>771534777884</Landline_ExtId>
<Landline_ExtId  action='add'>771534777885</Landline_ExtId>
<Landline_ExtId  action='add'>771534777886</Landline_ExtId>
<Landline_ExtId  action='add'>771534777887</Landline_ExtId>
<Landline_ExtId  action='add'>771534777888</Landline_ExtId>
<Landline_ExtId  action='add'>771534777889</Landline_ExtId>
<Landline_ExtId  action='del'>551534882800</Landline_ExtId>
<Landline_ExtId  action='del'>551534882801</Landline_ExtId>
<Landline_ExtId  action='del'>551534882802</Landline_ExtId>
<Landline_ExtId  action='del'>551534882803</Landline_ExtId>
<Landline_ExtId  action='del'>551534882804</Landline_ExtId>
<Landline_ExtId  action='del'>551534882805</Landline_ExtId>
<Landline_ExtId  action='del'>551534882806</Landline_ExtId>
<Landline_ExtId  action='del'>551534882807</Landline_ExtId>
<Landline_ExtId  action='del'>551534882808</Landline_ExtId>
<Landline_ExtId  action='del'>551534882809</Landline_ExtId>

XSLT:

           <?xml version="1.0" encoding="UTF-8"?>
    <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
      <xsl:template match="/">
    <xsl:element name="getMaxOld">
     <xsl:value-of select="/Data/Landline_ExtId[not(. &lt;      /Data/Landline_ExtId[@action='del'])][1]"/>
      </xsl:element>
     <xsl:element name="getMinOld">
    <xsl:value-of select="/Data/Landline_ExtId[not(. &gt; /Data/Landline_ExtId[@action='del'])][1]"/>
       </xsl:element>
           <xsl:element name="getMaxNew">
         <xsl:value-of select="/Data/Landline_ExtId[not(. &lt; /Data/Landline_ExtId[@action='add'])][1]"/>
       </xsl:element>
       <xsl:element name="getMinNew">
    <xsl:value-of select="/Data/Landline_ExtId[not(. &gt; /Da    ta/Landline_ExtId[@action='add'])][1]"/>
     </xsl:element>
</xsl:template>


    </xsl:stylesheet>

GetMaxOld の値が間違っています。551534882809 の代わりに 771534777880 が返されています