--- a/src/frame-x.c	Mon Aug 13 10:55:35 2007 +0200
+++ b/src/frame-x.c	Mon Aug 13 10:56:21 2007 +0200
@@ -103,19 +103,34 @@
 struct frame *
 x_any_window_to_frame (struct device *d, Window wdesc)
 {
+  Widget w;
+  assert (DEVICE_X_P (d));
+
+  w = XtWindowToWidget (DEVICE_X_DISPLAY (d), wdesc);
+
+  if (!w)
+    return 0;
+
+  /* We used to map over all frames here and then map over all widgets
+     belonging to that frame. However it turns out that this was very fragile
+     as it requires our display stuctures to be in sync _and_ that the 
+     loop is told about every new widget somebody adds. Therefore we
+     now let Xt find it for us (which does a bottom-up search which
+     could even be faster) */
+  return  x_any_widget_or_parent_to_frame (d, w);
+}
+
+static struct frame *
+x_find_frame_for_window (struct device *d, Window wdesc)
+{
   Lisp_Object tail, frame;
   struct frame *f;
-
-  assert (DEVICE_X_P (d));
-
   /* This function was previously written to accept only a window argument
      (and to loop over all devices looking for a matching window), but
      that is incorrect because window ID's are not unique across displays. */
 
   for (tail = DEVICE_FRAME_LIST (d); CONSP (tail); tail = XCDR (tail))
     {
-      int i;
-
       frame = XCAR (tail);
       f = XFRAME (frame);
       /* This frame matches if the window is any of its widgets. */
@@ -138,18 +153,18 @@
 	 would incorrectly get sucked away by Emacs if this function matched
 	 on psheet widgets. */
 
-      for (i = 0; i < FRAME_X_NUM_TOP_WIDGETS (f); i++)
-	{
-	  Widget wid = FRAME_X_TOP_WIDGETS (f)[i];
-	  if (wid && XtIsManaged (wid) && wdesc == XtWindow (wid))
-	    return f;
-	}
-
-#ifdef HAVE_SCROLLBARS
-      /* Match if the window is one of this frame's scrollbars. */
-      if (x_window_is_scrollbar (f, wdesc))
-	return f;
-#endif
+      /* Note: that this called only from
+         x_any_widget_or_parent_to_frame it is unnecessary to iterate
+         over the top level widgets. */
+
+      /* Note:  we use to special case scrollbars but this turns out to be a bad idea
+         because
+         1. We sometimes get events for _unmapped_ scrollbars and our
+         callers don't want us to fail.
+         2. Starting with the 21.2 widget stuff there are now loads of
+         widgets to check and it is easy to forget adding them in a loop here.
+         See x_any_window_to_frame
+         3. We pick up all widgets now anyway. */
     }
 
   return 0;
@@ -160,7 +175,7 @@
 {
   while (widget)
     {
-      struct frame *f = x_any_window_to_frame (d, XtWindow (widget));
+      struct frame *f = x_find_frame_for_window (d, XtWindow (widget));
       if (f)
 	return f;
       widget = XtParent (widget);