diff --git a/collects/frtime/frp-core.ss b/collects/frtime/frp-core.ss
index f3c43d53f8..6b5d165198 100644
--- a/collects/frtime/frp-core.ss
+++ b/collects/frtime/frp-core.ss
@@ -166,8 +166,9 @@
     (event-producer2
      (lambda (emit)
        (lambda the-args
-         (when (cons? the-args)
-           (emit (first the-args)))))))
+         (if (cons? the-args)
+             (emit (first the-args))
+             (make-events-now empty))))))
   
   (define (event-producer2 proc . deps)
     (let* ([result (apply proc->signal (lambda args (make-events-now empty)) deps)]
@@ -175,7 +176,8 @@
                        (lambda (val)
                          (let ([old-value (signal-value result)])
                            (make-events-now
-                            (if (= (current-logical-time) (event-set-time old-value))
+                            (if (and (event-set? old-value)
+                                     (= (current-logical-time) (event-set-time old-value)))
                                 (append (event-set-events old-value) (list val))
                                 (list val))))))])
       (set-signal-thunk! result proc/emit)
@@ -327,7 +329,9 @@
 
   ; set-cell! : cell[a] a -> void
   (define (set-cell! ref beh)
-    (! man (make-external-event (list (list ((signal-thunk ref) #t) beh)))))
+    (if (man?)
+        (iq-enqueue (list ((signal-thunk ref) #t) beh))
+        (! man (make-external-event (list (list ((signal-thunk ref) #t) beh))))))
   
   
   (define-values (undefined undefined?)
@@ -641,7 +645,6 @@
          b
          (filter weak-box-value dependents)))))
   
-
   (define (update0 b)
     (match b
       [(and (? signal?)
@@ -652,27 +655,13 @@
        (let ([new-value (call-with-parameterization
                          params
                          thunk)])
-         (if (or (signal:unchanged? b)
-                 (not (or (boolean? new-value)
-                          (symbol? new-value)
-                          (number? new-value)
-                          (string? new-value)))
-                 (not (eq? value new-value)))
+         (when (or (signal:unchanged? b)
+                   (and (not (eq? value new-value))
+                        (or (not (event-set? new-value)) (cons? (event-set-events new-value))
+                            (not (event-set? value)))))
            (begin
-             #;(if (signal? new-value)
-                 (raise (make-exn:fail
-                         "signal from update thunk!!!"
-                         (signal-continuation-marks b))))
-             #;(printf "~n[~a]: ~a --> ~a~n" (cond
-                                         [(signal:switching? b) 'signal:switching]
-                                         [(signal:compound? b) 'signal:compound]
-                                         [(signal:unchanged? b) 'signal:unchanged]
-                                         [else 'signal])
-                     value new-value)
              (set-signal-value! b new-value)
-             (propagate b))
-           #;(parameterize ([print-struct #f])
-             (printf "~a ... ~a (~a)~n" value new-value b))))]
+             (propagate b))))]
       [_ (void)]))
   
   (define (update1 b a)
diff --git a/collects/frtime/lang-ext.ss b/collects/frtime/lang-ext.ss
index 1abc084040..4e824e6364 100644
--- a/collects/frtime/lang-ext.ss
+++ b/collects/frtime/lang-ext.ss
@@ -361,7 +361,7 @@
              [head last]
              [producer (proc->signal
                         (lambda ()
-                          (let* ([now (and (behavior? consumer) (current-inexact-milliseconds))]
+                          (let* ([now (and (signal? consumer) (current-inexact-milliseconds))]
                                  [ms (value-now ms-b)])
                             (let loop ()
                               (if (or (empty? (mcdr head))
@@ -398,7 +398,7 @@
                [last-time (current-inexact-milliseconds)]
                [last-val (value-now b)]
                [last-alarm 0]
-               [producer (proc->signal (lambda () (and (behavior? consumer) accum)))]
+               [producer (proc->signal (lambda () (and (signal? consumer) accum)))]
                [consumer (proc->signal void b ms-b)])
         (set-signal-thunk!
          consumer
@@ -627,8 +627,9 @@
                      (send-event
                       (hash-table-get ht (fn e) (lambda () (k (void))))
                       e)))
-                 ht)])                             
+                 ht)])
       (lambda (x)
+        sig
         (hash-table-get
          ht x (lambda ()
                 (let ([rtn (event-receiver)])
diff --git a/collects/frtime/list.ss b/collects/frtime/list.ss
index 7a3b4bce9c..59027e8211 100644
--- a/collects/frtime/list.ss
+++ b/collects/frtime/list.ss
@@ -149,10 +149,15 @@
 
   
   (define (filter f l)
-    (cond
-      [(empty? l) empty]
-      [(f (first l)) (cons (first l) (filter f (rest l)))]
-      [else (filter f (rest l))]))
+    (list-match
+     l
+     (lambda (a d) (if (f a)
+                       (cons a (filter f d))
+                       (filter f d)))
+     (lambda () empty)))
+;      [(empty? l) empty]
+;      [(f (first l)) (cons (first l) (filter f (rest l)))]
+;      [else (filter f (rest l))]))
   
   
   (define (cons? x) (pair? x))
diff --git a/collects/frtime/mzscheme-core.ss b/collects/frtime/mzscheme-core.ss
index a2fd79beef..0f88d07c23 100644
--- a/collects/frtime/mzscheme-core.ss
+++ b/collects/frtime/mzscheme-core.ss
@@ -298,31 +298,30 @@
          (lambda ()
            (begin0
              (let/ec esc
-               (with-handlers ([exn:fail? (lambda (exn) #f)])
+               (begin0
+                 ;;(with-handlers ([exn:fail? (lambda (exn) #f)])
                  (proc (lambda (obj)
                          (if (behavior? obj)
                              (begin
                                (case (hash-table-get deps obj 'absent)
                                  [(absent) (hash-table-put! deps obj 'new)
-                                           (register rtn obj)
-                                           (iq-enqueue rtn)
-                                           (esc #f)]
+                                           (let ([o-depth (signal-depth rtn)])
+                                             (register rtn obj)
+                                             (when (> (signal-depth rtn) o-depth)
+                                               (iq-enqueue rtn)
+                                               (esc #f)))]
                                  [(old)    (hash-table-put! deps obj 'alive)]
                                  [(new)    (void)])
                                (value-now obj))
-                             obj))))
-               (hash-table-for-each
-                deps
-                (lambda (k v)
-                  (case v
-                    [(new)   (hash-table-put! deps k 'old)
-                             #;(printf "reg~n")
-                             (register rtn k)]
-                    [(alive) (hash-table-put! deps k 'old)]
-                    [(old)   (hash-table-remove! deps k)
-                             #;(printf "unreg~n")
-                             (unregister rtn k)])))
-               #;(printf "count = ~a~n" (hash-table-count deps)))))))
+                             obj)));)
+                 (hash-table-for-each
+                  deps
+                  (lambda (k v)
+                    (case v
+                      [(new alive) (hash-table-put! deps k 'old)]
+                      [(old)   (hash-table-remove! deps k)
+                               (unregister rtn k)])))
+                 #;(printf "count = ~a~n" (hash-table-count deps))))))))
       (iq-enqueue rtn)
       rtn))
   
@@ -389,7 +388,7 @@
          [(undefined? lst) undefined]
          [(pair? lst) (cf (first lst) (rest lst))]
          [(empty? lst) (ef)]
-         [else (error "list-match: expected a list but got" lst)]))
+         [else (error "list-match: expected a list, got ~a" lst)]))
      lst))
   
   #;(define (frp:append . args)