opAssign and const?

[Era Scarecrow]

  I have the following dilemma. Hopefully I have this right.

struct X {
   ref X opAssign(X x2);
   ref X opAssign(ref X x2);
}

X fn();

void func(){
   X x, x2;

   x = x2; //uses ref
   x = fn(); //without ref
}

  According to the book, this is how it is suppose to be. const is 
a added promise not to modify anything. So... if i changed the 
ref to ref const... it won't call unless the item input was const 
as well.

//same as above except..
struct X {
   ref X opAssign(X x2);
   ref X opAssign(ref const X x2); //const added
}

void func(){
   X x, x2;
   const X x3;

   x = x2; //without ref???
   x = x3; //ref
}

  Since the input is intended to be read only anyways, why won't 
it work as expected with x = x2? This seems like a bug. If it's 
not, then I need to make two ref versions so it will behave 
properly. (If you need I can past actual working example)