Take a look at the actual XSL-FO file and see whether the file names are incorrect there, just to verify that it's the XSLT processor that's getting it wrong.
Use system-property('xsl:vendor') somewhere in the stylesheet to see what XSLT processor you are using.
If the XSLT processor really is getting it wrong (not that unlikely, it's a rarely-used function) then send them a bug report.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference