This bug report is about using the functions position() and last() in the 'use' attribute of an 'xsl:key' element.
In the XSLT 2.0 specification in http://www.w3.org/TR/xslt20/#keys in the section starting with "The result of the key function can be described" it is said that the key specifier (i.e. the expression specified in the 'use' attribute of xsl:key) "is evaluated with a singleton focus". Singleton focus means that the context size is always 1 which means both the position() and the last() call in a 'use' expression should always return 1.
That however is currently not the case with your XSLT 2.0 processor, when I have input.xml as
1 2 3
and the stylesheet sheet.xsl as
then the result with your XSLT 2.0 processor is as follows:
<?xml version="1.0" encoding="UTF-8"?> 1 2 3 1 2 3
which shows that the 'use' expression is not executed with a singleton focus with context size 1 but rather with context size 3 which is a bug.