change the namespace of an element with xslt

I'd like to make this

<hello>
  <one>
    <paragraph>p1</paragraph>
  </one>
</hello> 

into this

<x:hello y:an_attribute="a value for an_attribute" xmlns:x="some_new_namespace" xmlns:y="other_ns">
  <one>
    <paragraph>p1</paragraph>
  </one>
</x:hello> 

this is the stylesheet I came up with:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="xml" indent="yes"/>

    <xsl:param name="element_localname" select="'hello'"/>


    <xsl:template match="node()">
        <xsl:choose>
            <xsl:when test="local-name() = $element_localname">
                <xsl:element name="{$element_localname}" namespace="some_new_namespace">
                    <xsl:attribute name="an_attribute" namespace="other_ns">a value for an_attribute</xsl:attribute>
                    <xsl:apply-templates select="node()"/>
                </xsl:element>
            </xsl:when>

            <!-- copy the rest as is -->
            <xsl:otherwise> 
                <xsl:copy>
                    <xsl:apply-templates select="node()" />
                </xsl:copy>
            </xsl:otherwise>

        </xsl:choose>
    </xsl:template>

</xsl:stylesheet> 

but for some strange reason, the attribute I am adding to the element has the same namespace as the root element itself? why?

<ns0:hello xmlns:ns0="other_ns" ns0:an_attribute="a value for an_attribute">
  <one>
    <paragraph>p1</paragraph>
  </one>
</ns0:hello>

Thank you for reading.