The JS glue just passes along whatever document.evaluate returns, after converting that array-like XPathResults list into a plain array:

    function(doc,q,ref,cont) {
        var xres = doc.evaluate(q,ref,null,XPathResult.ORDERED_NODE_SN
+APSHOT_TYPE, null );
        var map;
        if( cont ) {
            map = cont;
        } else {
            // Default is identity
            map = function(e){ return e };
        };
        var res = [];
        for ( var i=0 ; i < xres.snapshotLength; i++ )
        {
            res.push( map(xres.snapshotItem(i)));
        };
        return res
    }
[download]

I'm no expert on XPath and its semantics, but if somebody submits a bug report and preferrably a self-contained example, I can investigate things closer.