There's a non-normative table in section 5.4.4 that says the values of the 
current group and current grouping key components are cleared by calls on 
stylesheet functions.  But the sections on the current group, current grouping 
key, and xsl:for-each-group don't say anything about it.

This can be fixed with an editorial correction by adding just before the last 
sentence in 14.3, "During the evaluation of a stylesheet function, the current 
group and current grouping key are set to the empty sequence, and revert to 
their previous values on completion of evaluation of the stylesheet function."