disable-output-escaping in xsl:attribute

Ji!
I've got the following source:
<xsl:element name="span">
 <xsl:attribute name="title">
  <xsl:text disable-output-escaping="yes">G&auml;ste</xsl:text>
 </xsl:attribute>
 <xsl:text disable-output-escaping="yes">G&auml;ste</xsl:text>
</xsl:element>

Then I process it via PHP (and Sablotron 1.0) and it produces: 
'<span title="G&amp;auml;ste">G&auml;ste</span>' instead of the expected 
'<span title="G&auml;ste">G&auml;ste</span>'.

How can I fix this?

thanks,

 Stefan