function overload with mixin template bug?

[Patric Dexheimer via Digitalmars-d-learn]

1)

struct T{
    void f1(){writeln("default f1");}
    void f1(int x){writeln("overload f1");}
}
//main
T().f1();
T().f1(1);
//compiles and output as expected.

2)

mixin template add_function(){
    void f1(){writeln("default f1");}
}
struct T{
    mixin add_function;
    void f1(int x){writeln("overload f1");}
}
//main
T().f1();
T().f1(1);
//Error: function f355.T.f1 (int x) is not callable using 
argument types ()
/* What? i´m missing something here? */


3)

mixin template add_function(){
    void f1(){writeln("default f1");}
}
struct T{
    mixin add_function;
}
//main
T().f1();
//compiles and output as expected.


Function overloads coming from mixin templates are not being 
detected ?