Visibility of private parts

[ehsjony@ehs.ericsson.se (Jonas Nygren)]

I believed that your private parts were hidden in Ada.

Though, the function Bs.Something manages to call 
As.As_Private_Parts though it is a private type 
with a private procedure in the short example below.

package As is
   type A is private;
private
   type A is tagged null record;
   procedure As_Private_Parts (An_A : in out A);
end As;

with As;
package Bs is
   type B is new As.A;
   procedure Something (A_B : in out B);
end Bs;

package body Bs is 
   procedure Something (A_B : in out B) is
   begin
      As_Private_Parts(A_B);
   end Something;
end Bs;

Compiling bs.adb does not report any error - how can that be?

Should B be allowed to see A's private parts?
Is it a feature or a bug?

/jonas