DOCBOOK-APPS: Biblio: Abbrev only when first

Hi list,
The style contains the following (fo/biblio.xsl):
    <xsl:when test="local-name($node/child::*[1]) = 'abbrev'">

Is there a reason for this? 
It results in the <abbrev> value being displayed as the first element of
the corresponding entry in the bibliography section only when it is
written as the first tag in the biblioentry.

I exchanged it to this:
    <xsl:when test="$node/abbrev">

And now I get the abbrev, if I have one declared, no matter where it is
placed.

Stephan