exslt distinct() does not work with xalan compiled (but works in interpreted)

Question

I have this:

<xsl:message><xsl:copy-of select="set:distinct(//property)"/> </xsl:message>
<!--<xsl:message><xsl:copy-of select="set:distinct(common:node-set($mss)/indirect)"/> </xsl:message>-->

If I uncomment the second line, it does not work¹ when I use the stylesheet with compiled stylesheet in xalan.

It does work when I run xalan from the command line without -xsltc.

Am I doing something wrong?

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¹ I get some cryptic error message, and processing stops. Here is the error message for this instance: ERROR: '', but I got things like ERROR: -1 as well.

My <xsl:stylesheet> header contains xmlns:set="http://exslt.org/sets".