In the following example pred is shown as uncovered (tested in DrRacket 8.8 and 8.10).

#lang htdp/bsl

(define-struct S (pred))

(check-expect (S-pred (make-S #t)) #t)

If I manually select the language (and delete #lang), DrRacket indicates full coverage. Interestingly whatever emacs racket-mode is doing, it also indicates full coverage for the #lang version