A bad counterintuitive behaviour of Ada about OO

[Victor Porton <porton@narod.ru>]

http://freesoft.portonvictor.org/binaries/ada-obj-test.tar.gz

contains a tiny Ada program which prints 0 despite intuition suggests that 
it should print 123, because it just copies (using Adjust) an object holding 
123.

In this program Handle_Type models some handle provided by an external API, 
where 0 is an undefined handle. Base_Object is a tagged record which holds a 
handle inside itself and can copy or destroy the handle automatically (as 
Base_Object is a controlled object).

Example_Record is a derived type of Base_Object which imitates a behavior of 
a simple library which operates over some handles. For example, in this 
example copying a handle preserves it unchanged.

This tiny program was created by me as a model of my real Ada bindings for 
Raptor C library, which produces a wrong behavior.

Why Ada behaves in this counter-intuitive way?

What should I do in similar situations when developing real Ada software?

-- 
Victor Porton - http://portonvictor.org