winsamp.d and -O

[.]

The winsamp.d is distributed with DMD.  It's OK when being built like this:
   dmd winsamp gdi32.lib winsamp.def

However, running this:
   dmd -O winsamp gdi32.lib winsamp.def
will issue a error message:
   winsamp.d(35): Error: null dereference in function WindowProc

Check it, you will get this:
*(cast(int*) null) = 666;

Before firing a bug, I want to make sure about it.

Thanks.