GNAT: bug or feature?

[Damien Carbonne <damien.carbonne@free.fr>]

Hi,

When compiled with GNAT GPL 2009 or GNAT GCC 4.4.1 / Ubuntu 9.10, the 
following code:

---------------------------------------------------
package Pack07 is

    type Base is tagged null record;
    function Create return Base;

    type Derived is new Base with null record;

end Pack07;
---------------------------------------------------

exhibits different compiler reactions depending on used options.

With 'gcc -c -gnat95 pack07.ads', I get:

pack07.ads:6:09: type must be declared abstract or "Create" overridden
pack07.ads:6:09: "Create" has been inherited at line 6
pack07.ads:6:09: "Create" has been inherited from subprogram at line 4

This is what I expect.

With 'gcc -c -gnat05 pack07.ads", the compiler tells nothing and seems 
to generate code.

I find this surprising.
I would consider this is a compiler bug. Is this the case or is it a new 
Ada 2005 feature?
May be it is due to an installation problem, but it would be surprising.

What is your opinion about this behavior?

Regards,
Damien Carbonne