xsl:key not working when looping through nodeset obtained with xalan:nodeset

Question

I have found a case where xsl:key seems not to be working.
I am using XSLT 1 with Xalan (compiled) and this is what is happening:

1.- This works: key named test1 works fine:

<xsl:variable name="promosRTF">
  <xsl:copy-of select="promo[@valid='true']"/>
</xsl:variable>
<xsl:variable name="promos" select="xalan:nodeset($promosRTF)" />

<!-- now the key: when defined and used here it works fine: -->
<xsl:key name="test1" match="//promo" use="'anytext'" />
<xsl:for-each select="key('test1','anytext')/*">
  loop through elements in key... ok, works fine
</xsl:for-each>

<xsl:for-each select="$promos/*">
  ..loop through elements in variable $promos ...it is not empty so the loop iterates several times
</xsl:for-each>

2.- This doesn't work: key test1 is now defined and used (which is the important point, I guess) inside a loop that iterates through elements obtained with xalan:nodeset

<xsl:variable name="promosRTF">
  <xsl:copy-of select="promo[@valid='true']"/>
</xsl:variable>
<xsl:variable name="promos" select="xalan:nodeset($promosRTF)" />

<xsl:for-each select="$promos/*">
  <!-- now the key: when defined and used (or just used) inside this for-each loop it does nothing: -->
  <xsl:key name="test1" match="//promo" use="'anytext'" />
  <xsl:for-each select="key('test1','anytext')/*">
    loop through elements in key... NOTHING HERE, it does not work :(
  </xsl:for-each>

  ..loop through elements in variable $promos ...it is not empty so iterates several times
</xsl:for-each>

Does anybody know what is happening? Notice that variable $promos is not empty, so the loop really iterates, it is the key used inside it which does nothing.

Thank you very much in advance.

PS: after Martin's answer I post this alternative code, which doesn't work either:

<xsl:variable name="promosRTF">
  <xsl:copy-of select="promo[@valid='true']"/>
</xsl:variable>
<xsl:variable name="promos" select="xalan:nodeset($promosRTF)" />

<!-- now the key: defined as a first level element: -->
<xsl:key name="test1" match="//promo" use="'anytext'" />
<xsl:for-each select="$promos/*">
  <!-- but used inside this for-each loop it does nothing: -->
  <xsl:for-each select="key('test1','anytext')/*">
    loop through elements in key... NOTHING HERE, it does not work :(
  </xsl:for-each>

  ..loop through elements in variable $promos ...it is not empty so iterates several times
</xsl:for-each>

Solution: In Martin's comments was the key to the problem: nodes in a result tree fragment are treated as nodes in a different document.
Martin pointed the workaround too: In XSLT 1.0 you need to change the context node using a for-each and then call key inside the for-each. This code will work then:

<xsl:variable name="promosRTF">
  <xsl:copy-of select="promo[@valid='true']"/>
</xsl:variable>
<xsl:variable name="promos" select="xalan:nodeset($promosRTF)" />

<!-- now the key -->
<xsl:key name="test1" match="//promo" use="'anytext'" />
<xsl:for-each select="$promos/*">
  <!-- inside this for-each we are in a different *document*, so we must go back: -->
  <xsl:for-each select="/">
    <xsl:for-each select="key('test1','anytext')/*">
      loop through elements in key... and now IT WORKS, thanks Martin :)
    </xsl:for-each>
  </xsl:for-each>

  ..loop through elements in variable $promos ...it is not empty so iterates several times
</xsl:for-each>

Answer 1

I am surprised that you don't get an error by putting the xsl:key into the for-each. In http://www.w3.org/TR/xslt#key you can see that xsl:key is defined as a <!-- Category: top-level-element --> top level element so you need to put it as a child of xsl:stylesheet or xsl:transform.