(Struct st) does not work with polymorphic structs

What version of Racket are you using?

6.7.0.1

What program did you run?

#lang typed/racket
(struct (A) s1 ([f : A]))
(struct (A B) s2 s1 ([g : B]))
(struct s3 ([h : Symbol]))

(ann ((inst s2 Number String) 1 "b") (Struct s1)) ;; Error
(ann ((inst s2 Number String) 1 "b") (Struct s2)) ;; Error
(ann ((inst s2 Number String) 1 "b") (Struct (s1 Number))) ;; Works
(ann ((inst s2 Number String) 1 "b") (Struct (s2 Number String))) ;; Works
(ann (s3 'x) (Struct s3)) ;; Works

What should have happened?

The docs explicitly state that:

(Struct st) is a type which is a supertype of all instances of the potentially-polymorphic structure type st. Note that structure accessors for st will not accept (Struct st) as an argument.

so the first two cases should work, but they throw an error instead.

If you got an error message, please include it here.

Type Checker: parse error in type;
 expected a structure type for argument to Struct
  given: s1 in: (Struct s1)

and

Type Checker: parse error in type;
 expected a structure type for argument to Struct
  given: s2 in: (Struct s2)

Start by running the Typed Racket program in the issue and compare the two failing (Struct s1) and (Struct s2) annotations with the working parameterized forms. Done means the unparameterized polymorphic structure annotations are accepted as documented, while the existing working examples continue to pass.