call to super trashes pointer?

[Nicholas Wilson via Digitalmars-d-learn]

On Tuesday, 23 February 2016 at 09:16:08 UTC, Nicholas Wilson 
wrote:
> struct A
> {
> int blah;
> }
> class B
> {
>     A* a;
>     this(A* _a)
>     {
>         writeln(_a)
>         a =_a;
>     }
> }
>
> class C : B
> {
>     this(A* _a)
>     {
>         writeln(_a)
>         super(_a);
>     }
> }
> int main(string[] args)
> {
>         A a;
>         writeln(&a);
>         C c = new C(&a);
> }
>
> prints
> 7FFF56E787F8
> 7FFF56E787F8
> null
>
> ??? What is happening here?

fwiw I can reassign the reference (in the classes) to a after B's 
call to super but still ...