Pragma Unreferenced in GNAT GPL 2008

[Wilhelm Spickermann <quast.20.unbenutzbar@spamgourmet.com>]

After installing GNAT GPL 2008 I get unexpected warnings on
unreferenced variables:

...
      entry Wait (S : Event_State) when True is
      begin
         if S = On then
            requeue Wait_On with abort;
         else
            requeue Wait_Off with abort;
         end if;
      end Wait;

      entry Wait_On (S : Event_State) when Value = On is
         pragma Unreferenced (S);
      begin
         null;
      end Wait_On;
...
"pragma Unreferenced (S);" is honoured by GNAT GPL 2007 and seems
to be ignored by GNAT GPL 2008. 

Is this a compiler bug?

Wilhelm Spickermann