history为什么删除不掉

我的history信息如下：
                   List History File for dtw

Number of matching file entries = 1


Op Obj Timestamp+Sequence Type Dev Backup ID
-- --- ------------------ ---- --- --------------
  B  D  20140504012325001   F    N  
----------------------------------------------------------------------------
  Contains 18 tablespace(s):

00001 SYSCATSPACE
00002 USERSPACE1
00003 TBS_SML
00004 TBS_STK
00005 TBS_STKX
00006 TBS_CST
00007 TBS_CSTX
00008 TBS_HIS
00009 TBS_NO
00010 TBS_NOX
00011 TBS_O
00012 TBS_OX
00013 TBS_OL
00014 TBS_OLX
00015 TS8
00016 TS32
00017 SYSTOOLSPACE
00018 TS32X
----------------------------------------------------------------------------
Log Stream ID Earliest Log Current Log
------------- ------------ ------------
             0 S0000000.LOG S0000000.LOG
             1 S0000000.LOG S0000000.LOG
----------------------------------------------------------------------------
Comment: DB2 BACKUP DTW OFFLINE
Start Time: 20140504012325
   End Time: 20140504012345
     Status: A
----------------------------------------------------------------------------
  EID: 90 Location: /dev/null

我想把这条记录删除。

我执行prune命令，怎么还存在这条记录。
DB2>   db2 prune history 20140505 and delete
DB20000I  The PRUNE command completed successfully.