- in maybe_append_history, change check for history_lines_this_session
  so that we append the lines to the file if it's equal to the value
  returned by where_history(). This means that without this change,
  the history won't be appended if all the lines in the history list
  were added in the current session since the last time the history
  file was read or written. Fixes bug reported by Bruce Korb
  <[email protected]>

http://lists.gnu.org/archive/html/bug-bash/2010-08/msg00101.html

--- bashhist.c	2009-08-14 12:33:02.000000000 -0700
+++ bashhist.c	2013-08-26 02:05:33.384872000 -0700
@@ -372,7 +372,7 @@ maybe_append_history (filename)
   struct stat buf;
 
   result = EXECUTION_SUCCESS;
-  if (history_lines_this_session && (history_lines_this_session < where_history ()))
+  if (history_lines_this_session && (history_lines_this_session <= where_history ()))
     {
       /* If the filename was supplied, then create it if necessary. */
       if (stat (filename, &buf) == -1 && errno == ENOENT)