Well, Racket CS is "just" standard Racket running on Chez Scheme instead of the old Racket VM. Therefore no changes has been made to Racket (the language) - and

Well, Racket CS is "just" standard Racket running on Chez Scheme instead of the old Racket VM. Therefore no changes has been made to Racket (the language) - and thus there is no R7RS compatibility (which wasn't and still isn't a goal for Racket).