Welcome to the CHICKEN Scheme pasting service

(define (trick)
  (dynamic-wind (lambda () (print "before"))
                (lambda () (error 'foo))
                (lambda () (print "after"))))

;; calls before and after, no surprises:
(trick)

;; calls before only - why?
(thread-start! (lambda () (trick)))

;; calls before and after, no surprises
(thread-start!
 (lambda () (handle-exceptions e (raise e) (trick))))

fixed in 4.9rc1!

my mistake! this is still a problem in 4.9.0rc1!