For the following example,

  template<int N> struct A {};
  template<short N> using B = A<N>;
  template<int N> void f(B<N>) {} // #1
  template<int N> void f(A<N>) {} // #2

There is implementation variance as to whether there is one f or two. As with previously-discussed cases, these have different SFINAE effects, perhaps equivalent but not functionally equivalent. Should the argument to #1 be treated as something like A<(int)(short)N> and not just A<N>.

See also issues 1668 and 1979.