Inconsistent values from <xsl:variable/>

The use of an <xsl:if/> seem to result in different values being assigned:

  <xsl:variable name="RTF_GOOD">
      <xsl:value-of select="//out-form:Subform[@idType = 'RuleContent']"/>
  </xsl:variable>

  <xsl:variable name="RTF_BAD">
    <xsl:if test="2 > 1">
      <xsl:value-of select="//out-form:Subform[@idType = 'RuleContent']"/>
    </xsl:if>
  </xsl:variable>

Both have the same select="" expression; it's only the presence of the
<xsl:if/> that changes things.

 $RTF_GOOD appears to contain the RTF that I expect;

 $RTF_BAD appears to be a string containing the flattened text() from
    within the RTF I expect.

Any ideas why they differ ? Is this a bug in Xalan ? A bug in my
understanding of XSL is far more likely :>


--- Details ---

The above is a trivial example; I know about <xsl:variable select="..."/>,
but I need to do some conditional logic to determine exactly which
nodeset to place into my variable.)

(It may also be worth pointing out that I'm repeatedly using XPath on
 node-sets, along the lines of:

  <xsl:variable "foo"  select="//elem1"/>
  <xsl:variable "bar"  select="$foo//elem2"/>
  <xsl:variable "quux" select="$bar/[@attr = 'thing']"/>

 in case that explains anything ...)

I'm examining the contents using this:

  <xsl:message>GOOD
    <xsl:call-template name="dumpContext">
      <xsl:with-param name="myNodeSet" select="xalan:nodeset($RTF_GOOD)"/>
    </xsl:call-template>
  </xsl:message>

  <xsl:message>BAD
    <xsl:call-template name="dumpContext">
      <xsl:with-param name="myNodeSet" select="xalan:nodeset($RTF_BAD)"/>
    </xsl:call-template>
  </xsl:message>

  <xsl:template name="dumpContext">
    <xsl:param name="myNodeSet"/>
    <xsl:for-each select="$myNodeSet">
      <xsl:value-of select="local-name()"/>
      <xsl:text>[</xsl:text>
      <xsl:for-each select="ancestor-or-self::*">
        <xsl:text>/</xsl:text><xsl:value-of select="local-name()"/>
      </xsl:for-each>
      <xsl:text>]</xsl:text>
      <xsl:text>"</xsl:text>
      <xsl:value-of select="text()"/>
      <xsl:text>"</xsl:text>
    </xsl:for-each>
  </xsl:template>

And seeing output like this:

 Validation ERROR: GOOD Subform[/QueryResult/FormSet/Form/Thing/Subform]""]
 Validation ERROR: BAD  []"aaaaacoy3y0co110yy2005-01-012005-01-012005-01-03"]


Many (many !) thanks,

 - Adam