Any reason as to why this isn't allowed?

[Paul O'Neil via Digitalmars-d]

On 04/02/2016 09:02 AM, Lass Safin wrote:
> class C {
>          ~this() {}
>          immutable ~this() {}
> }
>
> This gives a conflict error between the two destructors.

What do you expect the difference to be?  I'm not sure what I expect the 
semantics of destroying an immutable object to be.