diff --git a/collects/2htdp/private/world.rkt b/collects/2htdp/private/world.rkt
index 162947c86a..b10b5f3ca6 100644
--- a/collects/2htdp/private/world.rkt
+++ b/collects/2htdp/private/world.rkt
@@ -50,23 +50,9 @@
    (clock-mixin
     (class* object% (start-stop<%>)
       (inspect #f)
-      
-      (init-field
-       world0            ;; World
-       (name #f)         ;; (U #f String)
-       (state #f)        ;; Boolean 
-       (register #f)     ;; (U #f IP)
-       (check-with True) ;; Any -> Boolean 
-       )
-      
-      (init
-       (on-key K)        ;; World KeyEvent -> World 
-       (on-release K)    ;; World KeyEvent -> World 
-       (on-mouse K)      ;; World Nat Nat MouseEvent -> World 
-       (on-receive #f)   ;; (U #f (World S-expression -> World))
-       (on-draw #f)      ;; (U #f (World -> Scene) (list (World -> Scene) Nat Nat))
-       (stop-when False) ;; World -> Boolean 
-       (record? #f))     ;; Boolean 
+      (init-field world0)
+      (init-field name state register check-with on-key on-mouse)
+      (init on-release on-receive on-draw stop-when record?)
       
       ;; -----------------------------------------------------------------------
       (field
@@ -159,6 +145,29 @@
           (create-frame)
           (show fst-scene)))
       
+      (define/private (deal-with-key %)
+        (if (not on-key) %
+            (class %
+              (super-new)
+              (define/override (on-char e) 
+                (when live
+                  (let ([e:str (key-event->parts e)])
+                    (if (string=? e:str "release")
+                        (prelease (key-release->parts e))
+                        (pkey e:str))))))))
+      
+      (define/private (deal-with-mouse %)
+        (if (not on-mouse) %
+            (class %
+              (super-new)
+              (define/override (on-event e)
+                (define-values (x y me) (mouse-event->parts e))
+                (when live
+                  (cond
+                    [(and (<= 0 x width) (<= 0 y height)) (pmouse x y me)]
+                    [(member me '("leave" "enter")) (pmouse x y me)]
+                    [else (void)]))))))
+      
       ;; effect: create, show and set the-frame
       (define/pubment (create-frame)
         (define play-back:cust (make-custodian))
@@ -170,24 +179,9 @@
                            (label (if name (format "~a" name) "World"))
                            (alignment '(center center))
                            (style '(no-resize-border metal))))
-        (define editor-canvas 
-          (new (class editor-canvas%
-                 (super-new)
-                 ;; deal with keyboard events 
-                 (define/override (on-char e) 
-                   (when live
-                     (let ([e:str (key-event->parts e)])
-                       (if (string=? e:str "release")
-                           (prelease (key-release->parts e))
-                           (pkey e:str)))))
-                 ;; deal with mouse events if live and within range 
-                 (define/override (on-event e)
-                   (define-values (x y me) (mouse-event->parts e))
-                   (when live
-                     (cond
-                       [(and (<= 0 x width) (<= 0 y height)) (pmouse x y me)]
-                       [(member me '("leave" "enter")) (pmouse x y me)]
-                       [else (void)]))))
+        
+        (define editor-canvas
+          (new (deal-with-key (deal-with-mouse editor-canvas%))
                (parent frame)
                (editor visible)
                (stretchable-width #f)
diff --git a/collects/2htdp/tests/jpr-bug.rkt b/collects/2htdp/tests/jpr-bug.rkt
new file mode 100644
index 0000000000..7ef0599af8
--- /dev/null
+++ b/collects/2htdp/tests/jpr-bug.rkt
@@ -0,0 +1,26 @@
+;; The first three lines of this file were inserted by DrRacket. They record metadata
+;; about the language level of this file in a form that our tools can easily process.
+#reader(lib "htdp-advanced-reader.ss" "lang")((modname jpr-bug) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #t #t none #f ())))
+
+;; This program demonstrated that the idea of using default handlers (K) for 
+;; absent mouse and key handlers was a horrible idea. The balls on his cannvas
+;; just started jumping around when the mouse moved in. 
+
+(require 2htdp/universe)
+(require 2htdp/image)
+
+
+(define (animation2)
+  (local [(define SIZE 300)
+          (define SCENE (rectangle SIZE SIZE 'outline "black"))
+          (define dM 1)
+          (define INIT 0)
+          (define (suivant m)
+            (+ m dM))
+          (define (dessiner m)
+            (place-image (circle m 'solid "red") (random SIZE) (random SIZE) SCENE))]
+    (big-bang INIT
+              (on-tick suivant 1)
+              (on-draw dessiner SIZE SIZE))))
+
+(animation2)
\ No newline at end of file
diff --git a/collects/2htdp/universe.rkt b/collects/2htdp/universe.rkt
index cac34c0d35..838941f28f 100644
--- a/collects/2htdp/universe.rkt
+++ b/collects/2htdp/universe.rkt
@@ -3,6 +3,8 @@
 ;; DONT USE to-draw IN THIS FILE 
 
 #| TODO: 
+   -- check that on-release is only defined if on-key is defined 
+
    -- yield instead of sync
    -- run callbacks in user eventspace
    -- make timer fire just once; restart after on-tick callback finishes
@@ -41,31 +43,29 @@
 (define new-universe (create-universe universe0))
 
 (define-keywords AllSpec '() define-all
-  ;; -- on-tick must specify a tick handler; it may specify a clock-tick rate
-  [on-tick   
-   DEFAULT #'#f
-   (function-with-arity
-    1 
-    except
-    [(_ f rate) 
-     #'(list 
-        (proc> 'on-tick (f2h f) 1)
-        (num> 'on-tick rate (lambda (x) (and (real? x) (positive? x)))
-              "positive number" "rate"))])]
+  ;; -- on-tick must specify a tick handler: World -> World 
+  ;; it may specify a clock-tick rate
+  [on-tick DEFAULT #'#f
+           (function-with-arity
+            1 
+            except
+            [(_ f rate) 
+             #'(list 
+                (proc> 'on-tick (f2h f) 1)
+                (num> 'on-tick rate (lambda (x) (and (real? x) (positive? x)))
+                      "positive number" "rate"))])]
   ;; -- state specifies whether to display the current state 
-  [state
-   DEFAULT #'#f
-   (expr-with-check bool> "expected a boolean (show state or not)")]
-  ;; -- check-with must specify a predicate 
-  [check-with
-   DEFAULT #'True
-   (function-with-arity 1)])
+  [state DEFAULT #'#f (expr-with-check bool> "expected a boolean")]
+  ;; Any -> Boolean 
+  ;; -- check-with: all states should specify this predicate 
+  [check-with DEFAULT #'True (function-with-arity 1)])
 
 ;  (create-world world0)
 (define-keywords WldSpec AllSpec create-world
-  ;; -- on-draw must specify a rendering function; it may specify dimensions
-  [on-draw to-draw
-           DEFAULT #'#f
+  ;; (U #f (World -> Scene) (list (World -> Scene) Nat Nat))
+  ;; on-draw must specify a rendering function; 
+  ;;   it may specify dimensions
+  [on-draw to-draw DEFAULT #'#f
            (function-with-arity 
             1 
             except
@@ -73,42 +73,36 @@
              #'(list (proc> 'to-draw (f2h f) 1) 
                      (nat> 'to-draw width "width")
                      (nat> 'to-draw height "height"))])]
-  ;; -- on-mouse must specify a mouse event handler 
-  [on-mouse
-   DEFAULT #'K
-   (function-with-arity 4)]
-  ;; -- on-key must specify a key event handler 
-  [on-key
-   DEFAULT #'K
-   (function-with-arity 2)]
-  ;; -- on-release must specify a release event handler 
-  [on-release
-   DEFAULT #'K
-   (function-with-arity 2)]
+  ;; World Nat Nat MouseEvent -> World 
+  ;; on-mouse must specify a mouse event handler 
+  [on-mouse DEFAULT #f (function-with-arity 4)]
+  ;; World KeyEvent -> World 
+  ;; on-key must specify a key event handler 
+  [on-key DEFAULT #f (function-with-arity 2)]
+  ;; World KeyEvent -> World 
+  ;; on-release must specify a release event handler 
+  [on-release DEFAULT #'K (function-with-arity 2)]
+  ;; (U #f (World S-expression -> World))
   ;; -- on-receive must specify a receive handler 
-  [on-receive
-   DEFAULT #'#f
-   (function-with-arity 2)]
+  [on-receive DEFAULT #'#f (function-with-arity 2)]
+  ;; World -> Boolean 
   ;; -- stop-when must specify a predicate; it may specify a rendering function
-  [stop-when
-   DEFAULT #'False
-   (function-with-arity 
-    1
-    except
-    [(_ stop? last-picture)
-     #'(list (proc> 'stop-when (f2h stop?) 1)
-             (proc> 'stop-when (f2h last-picture) 1))])]
+  [stop-when DEFAULT #'False
+             (function-with-arity 
+              1
+              except
+              [(_ stop? last-picture)
+               #'(list (proc> 'stop-when (f2h stop?) 1)
+                       (proc> 'stop-when (f2h last-picture) 1))])]
+  ;; (U #f Boolean)
   ;; -- should the session be recorded and turned into PNGs and an animated GIF
-  [record?
-   DEFAULT #'#f
-   (expr-with-check bool> "expected a boolean (to record? or not)")]
-  [name
-   DEFAULT #'#f
-   (expr-with-check string> "expected a name (string) for the world")]
+  [record? DEFAULT #'#f (expr-with-check bool> "expected a boolean")]
+  ;; (U #f String)
+  ;; -- name specifies one string 
+  [name DEFAULT #'#f (expr-with-check string> "expected a string")]
+  ;; (U #f IP)  
   ;; -- register must specify the internet address of a host (e.g., LOCALHOST)
-  [register
-   DEFAULT #'#f
-   (expr-with-check ip> "expected a host (ip address)")])
+  [register DEFAULT #'#f (expr-with-check ip> "expected a host (ip address)")])
 
 ;  (create-universe universe0)
 (define-keywords UniSpec AllSpec create-universe
@@ -155,15 +149,15 @@
          )
 
 (provide-primitives
-         make-package ;; World Sexp -> Package
-         package?     ;; Any -> Boolean 
-         run-movie    ;; [Listof Image] -> true 
-         mouse-event?  ;; Any -> Boolean : MOUSE-EVTS
-         mouse=?       ;; MOUSE-EVTS MOUSE-EVTS -> Boolean 
-         key-event?    ;; Any -> Boolean : KEY-EVTS
-         key=?         ;; KEY-EVTS KEY-EVTS -> Boolean
-         ;; IP : a string that points to a machine on the net 
-         )
+ make-package ;; World Sexp -> Package
+ package?     ;; Any -> Boolean 
+ run-movie    ;; [Listof Image] -> true 
+ mouse-event?  ;; Any -> Boolean : MOUSE-EVTS
+ mouse=?       ;; MOUSE-EVTS MOUSE-EVTS -> Boolean 
+ key-event?    ;; Any -> Boolean : KEY-EVTS
+ key=?         ;; KEY-EVTS KEY-EVTS -> Boolean
+ ;; IP : a string that points to a machine on the net 
+ )
 
 (provide LOCALHOST     ;; IP
          )