=== modified file 'src/window.c'
--- src/window.c	2013-02-01 07:23:18 +0000
+++ src/window.c	2013-02-07 05:31:20 +0000
@@ -269,9 +269,10 @@
 }
 
 /* Called when W's buffer slot is changed.  ARG -1 means that W is about to
-   cease its buffer, and 1 means that W is about to set up the new one.  */
+   cease its buffer, and 1 means that W is about to set up the new one.
+   Return W's buffer if it's a buffer or NULL otherwise.  */
 
-static void
+static struct buffer *
 adjust_window_count (struct window *w, int arg)
 {
   eassert (eabs (arg) == 1);
@@ -283,21 +284,34 @@
 	b = b->base_buffer;
       b->window_count += arg;
       eassert (b->window_count >= 0);
-      /* These should be recalculated by redisplay code.  */
-      w->window_end_valid = 0;
-      w->base_line_pos = 0;
+      return b;
     }
+  return NULL;
 }
 
-/* Set W's buffer slot to VAL and recompute number
-   of windows showing VAL if it is a buffer.  */
+/* Set W's buffer slot to VAL and recompute number of windows showing
+   VAL if it is a buffer, catch some redisplay's attention if needed.  */
 
 void
 wset_buffer (struct window *w, Lisp_Object val)
 {
-  adjust_window_count (w, -1);
+  struct buffer *oldb, *newb;
+
+  oldb = adjust_window_count (w, -1);
   w->buffer = val;
-  adjust_window_count (w, 1);
+  newb = adjust_window_count (w, 1);
+  if ((oldb && oldb == newb
+       && ((BUF_UNCHANGED_MODIFIED (oldb) < BUF_MODIFF (oldb))
+	   || (BUF_OVERLAY_UNCHANGED_MODIFIED (oldb)
+	       < BUF_OVERLAY_MODIFF (oldb))))
+      || (!oldb && newb))
+    {
+      /* If W's buffer was changed since last redisplay or W
+	 is switched to another buffer from no buffer, next
+	 redisplay should recalculate these fields.  */
+      w->window_end_valid = 0;
+      w->base_line_pos = 0;
+    }
 }
 
 /* Build a frequently used 4-integer (X Y W H) list.  */