DOCBOOK: Saxon and autoidx.xsl?

Using autoidx.xsl in version 1.37 of the stylesheets and Saxon 6.2, I
get the following error:

     [java] Failed to compile style sheet
     [java] At xsl:key on line 47 of
file:/C:/docbuild/TestDoc/../ThirdParty/DocBookXSL/docbook/fo/autoidx.xs
l: The expressions in xsl:key may not contain references to variables

autoidx.xsl works fine with Xalan-J 2.0.1 and Xalan-C 1.1.

Perhaps there's a switch I need to set somewhere? 

Thanks,
David

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