13.10.3.6 [temp.deduct.type] paragraph 22 describes how we cope with partial ordering between two function templates that differ because one has a function parameter pack while the other has a normal function parameter. However, this paragraph was meant to apply to template parameter packs as well, e.g., to help with partial ordering of class template partial specializations:

   template <class T1, class ...Z> class S; // #1
   template <class T1, class ...Z> class S<T1, const Z&...> {}; // #2
   template <class T1, class T2> class S<T1, const T2&> {};; // #3
   S<int, const int&> s; // both #2 and #3 match; #3 is more specialized

(See also issue 818.)