Days ago i started reading about continuations and delimited continuation control operators in Scheme (i’m working in racket but using scheme continuations). In that context i was trying the shift/reset operators implementation in terms of call/cc according of this paper. The code works as expected:

(define-syntax reset
  (syntax-rules ()
    ((reset ?e ...) (*reset (lambda () ?e ...)))))

(define-syntax shift
  (syntax-rules ()
    ((shift ?k ?e ...) (*shift (lambda (?k) ?e ...)))))

(define-syntax abort
  (syntax-rules ()
    ((abort ?e ...) (*abort (lambda () ?e ...)))))


(define (*abort _thunk)
    ((lambda (v) (*meta-continuation* v))  (_thunk)))

(define (*meta-continuation* v)
  (error "You forgot the top-level reset..."))

(define (*abort _thunk)
    ((lambda (v) (*meta-continuation* v))  (_thunk)))  ;; <- the line i'm asking for

(define (*reset thunk)
  (let ((mc *meta-continuation*))
    (call-with-current-continuation2
     (lambda (k)
       (set! *meta-continuation*
             (lambda (v)
               (set! *meta-continuation* mc) 
               (k v)))
       (abort (thunk))))))

(define (*shift f)
  (call-with-current-continuation2
   (lambda (k) (abort (f (lambda (v) (reset (k v))))))))

;; PROGRAM STARTS HERE
(+ 1 (reset (* 2 (shift k (k (k 4)))))) ; should be 17

First, macros for reset, shift and abort are defined with simply wraps the arguments in lambdas, then the proper *abort, *reset and *shift functions are defined.
however i had bad times trying to understand the *abort function definition.

In particular, if i try to replace the code

((lambda (v) (*meta-continuation* v))  (_thunk)))

or this equivalent version in the paper that also works (let ((v (_thunk))) (*meta-continuation* v)) with a direct call :

(*meta-continuation* (_thunk))

the program no longer gives the correct result of 17 but 9 instead (as if the stored continuations in reset from nested shifts were discarded).

That is, I tend to think that binding the result of the call to _thunk (_thunk) to a variable v and then calling (*meta-continuation* v) should be the same as the call (*meta-continuation* (_thunk)). Even if (_thunk) or (*meta-continuation* ...) does not return because call/cc.
Is not in both cases (*meta_continuation* []) the continuation of (_thunk) ?

What am I not understanding here?

Thanks.