D structs weak identity and RAII

[Boris-Barboris via Digitalmars-d-learn]

Hello, I was trying to write some templated unique pointers.
Idea was simple: struct UniquePointer that handles underlying 
pointer in RAII-style and WeakPointer struct that is spawned by 
UniquePointer. Weak pointer is handled differently in my 
collections, wich subscribe to the event of UniquePointer 
destruction, so that there are no dangling references left all 
over the heap (I use Mallocator). Collection's insertFront\Back 
methods register callbacks in Weak pointer itself, and all 
existing weak pointers are registered in Unique pointer.

That, unfortunately, failed at the very beginning. Then I wrote a 
unit test to investigate:

https://dpaste.dzfl.pl/d77c72198095

1). line 47 and 76 together mean, that there is basically no 
reliable way to write uniqueptr method wich returns WeakPointer, 
registered by the correct pointer in it's constructor. Or is 
there? Is usage of &this in constructor (or in struct methods in 
general) fundamentally unreliable in D?
2). postblit was never called when returning struct from 
function. I noticed it was called once on line 91, if i removed 
opAssign with ref argument. What are the rules? Why is it always 
called when passing struct to function and creating local copy of 
the parameter (lines 113, 127, 139), and why is opAssign not 
called?
3). Is there a way to reliably encapsulate all assignments? Looks 
like complete mess will happen should I apply some std.algorithm 
functions on array of structs with overloaded operators.
4). Any suggested workarounds? I never tried it in C++, but, 
IIRC, struct life cycle is much more consistent there ang gives 
the strict control I desire.
5). If all this is a design choice, what is the reason behind it?