Grouping problem

I have the following XML file -
<?xml version="1.0" encoding="UTF-8"?>
<root>
   <a>1</a>
   <b>2</b>
   <d>3</d>
   <d>4</d>
   <b>5</b>
   <b>6</b>
   <c>7</c>
   <c>8</c>
   <a>9</a>
</root>

I am trying to do grouping operation with the following XSL -
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

	<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

	<xsl:template match="/root">
	   <groups>
  	     <xsl:for-each select="*[not(name() = name(preceding-sibling::*))]">
            <group name="{name()}" />
   	     </xsl:for-each>
	   </groups>
	</xsl:template>

</xsl:stylesheet>

I am expecting output -
<groups>
   <group name="a" />
   <group name="b" />
   <group name="c" />
   <group name="d" />
</groups>

But I get output -
<?xml version="1.0" encoding="UTF-8"?>
<groups>
<group name="a"/>
<group name="b"/>
<group name="d"/>
<group name="d"/>
<group name="b"/>
<group name="b"/>
<group name="c"/>
<group name="c"/>
</groups>

Where is the problem?

This is tested with Xalan-J 2.6.0 and Saxon 8.4

Regards,
Mukul