template specialization and template mixin

[Jack Applegame]

This code compiles , as expected
     struct A {
       void func(string s : "foo")() {
         pragma(msg, "func for foo");
       }
       void func(string s)() {
         pragma(msg, "func for others: " ~ s);
       }
     }

     void main() {
       A a;
       a.func!"foo"();
       a.func!"bar"();
     }
Why this doesn't compile?
     mixin template M() {
       void func(string s)() {
         pragma(msg, "func for others: " ~ s);
       }
     }

     struct A {
       mixin M;
       void func(string s : "foo")() {
         pragma(msg, "func for foo");
       }
     }

     void main() {
       A a;
       a.func!"foo"();
       a.func!"bar"(); // Error
     }