It seems to be this: https://msdn.microsoft.com/en-us/library/aa384249.aspx https://msdn.microsoft.com/en-us/library/aa384249.aspx "The primary reason is that

It seems to be this: https://msdn.microsoft.com/en-us/library/aa384249.aspx https://msdn.microsoft.com/en-us/library/aa384249.aspx "The primary reason is that handles have 32 significant bits on 64-bit Windows. Therefore, handles cannot be truncated and passed to 16-bit applications without loss of data."