Use std::stable_sort instead of std::sort. When xsl:sort specifies a numerical sort, but you've got some string data in there we need to maintain the relative of that string data. This is the first time I've actually used std::stable_sort. I will mark it down in my big book of programming accomplishments.

include/XSLT/impl/xslt_sort.hpp

@@ -165,7 +165,7 @@ protected:
     }
 
     sort_->set_context(node, context);
-    std::sort(nodes.begin(), nodes.end(), SortP(*sort_));
+    std::stable_sort(nodes.begin(), nodes.end(), SortP(*sort_));
   } // sort
 
   bool has_sort() const { return sort_ != 0; }