why are these unknown identifiers?

[ucivax!gateway@ucbvax.Berkeley.EDU (Jose Duarte)]

-----------------------------------------
package X is

	type DIRECTIONS is (UP,DOWN,LEFT,RIGHT);

end X;
-----------------------------------------
with X;
package Y is

	subtype DIRECTIONS is X.DIRECTIONS;

end Y;
-----------------------------------------
with TEXT_IO;
use  TEXT_IO;
with Y;
procedure BUG is

V1 : Y.Directions := Y.UP;    -- Y.UP is unknown
V2 : Y.Directions := Y.DOWN;  -- Y.DOWN is unknown

begin
  null;
end BUG;

Can someone tell me why "Y.UP" and "Y.DOWN" are unknown identifiers
within the procedure BUG? I have to "with X" and then assign X.UP
and X.DOWN to V1 and V2 in order to compile this. Why is this the case?
Is this an Ada pecularity or a compiler bug?


Thanks!
JOSE DUARTE