Static bounds of loop - compilation error

[pascal.malaise@gmail.com]

Hi Ada experts,

can anyone explain the following compilation errors:
procedure T is
  type E is (A, B, C);
  subtype S is E range A .. B;
  X, Y : S;
begin
  X := A;
  Y := B;
  for I in S range X .. Y loop
    case I is
      when A => null;
      when B => null;
    end case;
  end loop;
end T;
>> missing case value: "C"

A similar example where S is a subtype of Positive leads to the same  error and also: bounds of "I" are not static, alternatives must cover base type

Indeed, X and Y are not static but the bounds of S are, and all the values of S are covered in the "case".

So is it a bug?

Thank you