Bug in mixins?

[Frustrated]

Can someone check this out? The best I can acertain is that the 
mixin template isn't adding the generated functions because it 
thinks they are already in the class.

i.e., the code generates the following methods

@property iButton button(iButton b)
@property iBorder border(iBorder b)

and the class contains the methods

@property WindowsButton button()
@property WindowsButton button(WindowsButton b)

and the template mixin simply doesn't add the generic methods. 
(simply because mixing the string mixin directly works, wrapping 
it in a mixin template does not)

Using that I created a MWE:

http://dpaste.dzfl.pl/6f64e49aba95



import std.stdio, std.cstream;

// mixin template used to wrap the string mixin
mixin template C() { mixin(B); }

// eponymously named template used as a string mixin to generate 
the function
template B()
{
	string B() { return "void foo(iA a) { writeln(`Generic`);  }"; }
}

interface iA {	void foo(iA a); }

class A : iA
{
	void foo(A a) { writeln("Specific"); }
	//mixin(B);
	mixin C;    // doesn't work, use line above, does not insert 
generic foo
}


void main()
{
	iA a = new A;
	a.foo(a);
	(cast(A)a).foo(cast(A)a);
	(cast(A)a).foo(a);  // line doesn't work when using mixin 
template because the generic foo does not exist
}


This seems like a bug to me but maybe that's how mixin templates 
work? If so is there any way to make them insert the code 
regardless if it thinks they are the same? (they are not in this 
case and I need to use them to reduce redundancy)