Arrays of structs

[John Burton via Digitalmars-d-learn]

I'm a c++ programmer trying to understand how memory allocation 
works in D.

I created a struct and added a destructor to it. My understanding 
is that structs have deterministic destructors - they are called 
when the struct goes out of scope (unless it is allocated with 
new).

Now if I put instances of the struct in a fixed size array

data[6] d;
d[3] = data(1, 2, 3);

then the destructor on all the contents is called when the array 
goes out of scope.

However if I add them to a dynamic array...

data[] d;
d ~= data(1, 2, 3)

Then the destructor appears to be called at some random time 
later. So it looks like it's the garbage collection that is doing 
this. That seems to go against the specification of how struct 
works... I'm not creating the item with "new" and as far as I can 
tell the array is storing instances of objects, not pointers to 
objects?

Is my understanding correct?
Is it documented anywhere how memory allocation works for this?

Is a dynamic array in fact storing an array of GC'd pointers to 
the structs? Or something else...