[xsl] apply-templates repeats inside xsl:for-each, why

["Mark Giffin m1879@xxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

I'm running xsl:for-each on a variable $platforms that holds this:

      <platform name="windows_xp" id="unique_2"/>
      <platform name="windows_vista" id="unique_35"/>
      <platform name="windows_7" id="unique_37"/>

The following code produces the same output 3 times for each node in 
$platforms:

        <xsl:for-each select="$platforms/platform">
          <xsl:apply-templates 
select="$root-of-input-file/map/concept/concept[@id = @id]"/>
        </xsl:for-each>

So in the output I get this kind of thing:

Windows XP
Windows Vista
Windows 7
Windows XP
Windows Vista
Windows 7
Windows XP
Windows Vista
Windows 7

I was expecting to get one output for each element in $platforms. If I 
use the following outside of xsl:for-each, I get one output:

<xsl:apply-templates select="$root/map/concept/concept[@id = 'unique_2']"/>

What am I missing?

thanks,
Mark