Text_IO.Text_Streams causing errors

[Julian Leyh <julian@vgai.de>]

Hi, i have some code that looks like this (stripped to minimal
example):

-- bar.adb:
with Foo;
procedure Bar is
   Foobar : aliased Foo.Foobar;
begin
   Foo.Print (Foobar'Access, "Foobar");
end Bar;

-- foo.adb:
with Text_IO.Text_Streams;
package body Foo is
   procedure Print (This : access Foobar'Class; Prefix : in String) is
   begin
      Text_IO.Put_Line (Prefix);
   end Print;
end Foo;

-- foo.ads:
package Foo is
   type Foobar is tagged private;
   procedure Print (This : access Foobar'Class; Prefix : in String);
private
   type Foobar is tagged null record;
end Foo;

Compiling it, I get this error:

foo.adb:3:14: not fully conformant with declaration at foo.ads:3
foo.adb:3:14: type of "This" does not match

If I add -gnat05, the error disappears, and it disappears, too, if I
add the "Ada." prefix to the "with".

I know that I could remove the "Text_Streams", because it is not used
at all, but I'm still a big confused about this error.

Is it a compiler bug or did I do something forbidden?

Tried with compilers GNAT GPL 2010 and GNAT Pro 6.3.1