set:difference() using two different node sets

We're trying to use set:difference() to compare two separate node-sets that
we create in variables.  

Most of the examples I see for this use partial node-sets from the same
parent node and compare those to get the difference (See the example found
at: http://www.exslt.org/set/functions/difference/index.html).  My question
is do the two node sets need to have the same parent, or can they be from
two separate sources?

In effect we are doing something like:

<xsl:variable name="v1">
	<xsl:for-each select="document('set1.xml')/*">
		<node id="@someId"/>
	</xsl:for-each>
</xsl:variable>
<xsl:variable name="v2">
	<xsl:for-each select="document('set2.xml')/*">
		<node id="@id"/>
	</xsl:for-each>
</xsl:variable>

<xsl:copy-of select="set:difference(
				msxsl:node-set($v1), msxsl:node-set($v2))"/>

We are always getting the complete list found in $v1.  We're not sure if it
is by design or a problem with the implementation of set:difference.

PS: We're using the EXSLT.NET 1.1.1 as the implementor of the EXSLT
functions.

Thanks.

-- 
Kipp E. Howard
Sr. Software Engineer, LexisNexis File & Serve
Phone: 425.372.1837 or 800.774.7317 ext 1837
Email: [email protected]