Unexpected behavior when using both alias this and object pointer

[xiren7 via Digitalmars-d-learn]

The problem and the code:

import std.stdio: writeln;
import core.stdc.stdlib: malloc;
struct Impl {
    ubyte[8] payload;
}

class Foo {
    Impl *impl;
    alias impl this;

    this()
    {
        impl = cast(Impl*) malloc(Impl.sizeof);
    }
}

class Foo2 {
    ubyte[8] payload;
}

void main()
{
    // alias T = Foo2;
    alias T = Foo;

    auto t = new T();

    // what I want to do is:
    // 1. cast t as pointer
    // 2. passe the pointer to a extern(C) callback function
    // 3. cast the pointer back to t in extern(C) callback 
function
    // 4. accesse the payload field
    auto payload = (cast(T) cast(void*) t).payload; // -> crashs

    // the right way to get the address of the t object
    writeln(*cast(void**) &t);          // -> 278E3373000

    // the unexpected behavior
    // the obvious(but wrong) way to get the address of the t 
object
    writeln(cast(void*) t);             // -> 278E164DAB0

    // because of alias this
    // cast(void*) t == cast(void*) t.payload
    writeln(cast(void*) t.payload);     // -> 278E164DAB0
}

My question is should let the compiler generate a warning about 
this unexpected(maybe) behavior?