When is array-to-array cast legal, and what does actually happen?

[Ali Çehreli]

Is the following cast legal with dmd 2.040?

struct MyChar
{
     dchar d;

     this(dchar param)
     in {
         assert(false);       // not called
     }
     body
     {
         d = param;
         assert(d != param);  // not called
     }

     this(this)
     in {
         assert(false);       // not called
     }
     body
     {
         assert(d != d);      // not called
     }
}

void main()
{
     MyChar[] mine = cast(MyChar[])("hello"d);   // legal?
     assert(mine[0].d == 'h');
}

I see that neither the constructor nor the postblit is called. 
Apparently the bit representation is used. This has the risk of 
violating struct invariants.

Is it legal?

Thank you,
Ali