> On Apr 6, 2016, at 9:02 AM, Matthew Flatt <mfl...@cs.utah.edu> wrote:
> 
> If the problem happens after DrRacket has been running for a while,
> then that's good information and definitely a problem to investigate.

I can confirm that (after 3-5 hours of development work) the problem is back.

I also shortened the program down to about 36 lines (below). Finally, once 
again I restarted DrR and the problem went away.

I’ll go ahead and file a bug report, I guess.

Okay, done.

John


#lang racket

(require 2htdp/universe
        2htdp/image)

(define r (rectangle 40 40 'solid 'green))

;; represents a position on the screen
(struct posn (x y) #:transparent)

;; in seconds:
(define TRANSITION-TIME 1)

;; in frames per second
(define FRAME-RATE 40)

(define SCENEWIDTH 400)
(define SCENEHEIGHT 300)

(define transition-frames (* TRANSITION-TIME FRAME-RATE))

;; given frame number, overlay
;; image at the correct location
(define (draw-world w)
  (define frac (/ (modulo w transition-frames) transition-frames))
  (define 1-frac (- 1 frac))
  (place-image r (+ (* 1-frac 50) (* frac 100))
               (+ (* 1-frac 120) (* frac 115))
               bg-scene))

(define bg-scene (empty-scene SCENEWIDTH SCENEHEIGHT))

(big-bang 0
          [to-draw draw-world]
          [on-tick add1 (/ 1 FRAME-RATE)])



> 
> Thanks!



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