auto return type inheritance not covariant

[iLewis]

Maybe this has been brought up before, but i could find no previous submissions.

the following code compiles with the error "Error: function xxx.B.fn of type
() overrides but is not covariant with xxx.A.fn of type ()" even though they
both return an auto of type int... is this a bug or oversight by myself? I am
unable to find any documentation saying that this is illegal.

I realize its easy to fix by changing the return type to int, however i was
just curious.

class A
{
        auto fn()
        {
                return 10;
        }
}

class B : A
{
        auto fn()
        {
                return 5;
        }
}