This was reported as bug 486818 in debian, and I verified it applies to last release (1.1.22). Reading the spec, it seems to me the namespace declaration should be there. Even if I'm reading badly the spec, the behaviour between the two cases exposed shouldn't be different.

Here is the original report:

Example stylesheet: missing.xsl

<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xhtml="http://www.w3.org/1999/XHTML">

<xsl:template match="/">
  <xsl:element name="foo">
    <bar/>
  </xsl:element>
</xsl:template>

</xsl:stylesheet>

Let's apply it.

$xsltproc missing.xsl missing.xsl
<?xml version="1.0"?>
<foo><bar/></foo>

The output is wrong: the namespace prefix 'xhtml' should be declared on element
bar.

Using the following, equivalent stylesheet instead of the above:

<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xhtml="http://www.w3.org/1999/XHTML">

<xsl:template match="/">
  <xsl:element name="foo">
    <xsl:call-template name="bar"/>
  </xsl:element>
</xsl:template>

<xsl:template name="bar">
  <bar/>
</xsl:template>
</xsl:stylesheet>

the output is

<?xml version="1.0"?>
<foo><bar xmlns:xhtml="http://www.w3.org/1999/XHTML"/></foo>

which is correct.