Fix bug #13108 introduced by the fix to bug #12930.

 src/indent.c (Fvertical_motion): If a display string will be
 displayed on the left or the right margin, don't consider it as a
 factor in cursor positioning.

src/ChangeLog

+2012-12-07  Eli Zaretskii  <eliz@gnu.org>
+
+	* indent.c (Fvertical_motion): If a display string will be
+	displayed on the left or the right margin, don't consider it as a
+	factor in cursor positioning.  (Bug#13108)
+
 2012-12-07  Martin Rudalics  <rudalics@gmx.at>
 	* editfns.c (Fcompare_buffer_substrings): Reword doc-string.

src/indent.c

@@ -2034,7 +2034,11 @@ whether or not it is currently displayed in some window.  */)
 	  const char *s = SSDATA (it.string);
 	  const char *e = s + SBYTES (it.string);
 
-	  disp_string_at_start_p = it.string_from_display_prop_p;
+	  /* If it.area is anything but TEXT_AREA, we need not bother
+	     about the display string, as it doesn't affect cursor
+	     positioning.  */
+	  disp_string_at_start_p =
+	    it.string_from_display_prop_p && it.area == TEXT_AREA;
 	  while (s < e)
 	    {
 	      if (*s++ == '\n')