> One more point. I re-wrote the key() function within the
> <xsl:apply-templates> element.
> 
> Original
> --------
> <xsl:apply-templates select="key('x',addressbook/address/zip)" />
> 
> Modified
> --------
> <xsl:apply-templates select="addressbook/address[key('x', zip)]" />
> 
> This time it worked.

Which means that your processor is correctly eliminating duplicates in the
result of a path expression, but is incorrectly failing to remove them in
the result of key().

Michael Kay
http://www.saxonica.com/