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?