Templated struct operator overloading

[Peter Alexander]

Is this a bug, or a limitation of how operator overloads handle generic 
operands?

  struct Vec(int N) {}
  struct Mat(int M, int N)
  {
      Vec!(M) opBinary(string op)(in Vec!(N) rhs)
      {
          return Vec!(M)();
      }
  }

  void main()
  {
      Vec!(3) v;
      Mat!(3, 3) m;

      Vec!(3) x = m * v; // Error: incompatible types for m * v
      Vec!(3) y = m.opBinary("*")(v); // Works
  }

Note that if you change the operator signature to:

  Vec!(3) opBinary(string op)(in Vec!(3) rhs)

then the first statement also compiles, but of course this makes the 
program incorrect.

Is this a bug or a language limitation?