Xtrabackup error when backup mysql 5.5.9 about data dictionary

during xtrabackup ( innobackupex-1.5.1 binary , mysql 5.5.9 file-format=Barracuda)

aplications do some action like truncate table

xtrabackup export some error :

[01] Copying ./cnt_it/cnt_goals_abandon_201109.ibd
to /usr/local/mysql/crontab/cnt_it/backup/innodb/full/2011-06-1 3_10-10-25/cnt_it/cnt_goals_abandon_201109.ibd
[01] …done
[01] Copying ./cnt_it/cnt_referrer_search_keyworInnoDB: Error: tablespace id is 46495 in the data dictionary
InnoDB: but in file ./cnt_it/cnt_referrer_summary_work.ibd it is 46506!
110613 10:36:28 InnoDB: Assertion failure in thread 1205774656 in file fil/fil0fil.c line 732
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.1/en/forcing-recovery.html
InnoDB: about forcing recovery.
to /usr/local/mysql/crontab/cnt_it/backup/innodb/full/2011-06-1 3_10-10-25/cnt_it/cnt_referrer_search_keyword_201107.ibd
[01] …done
[01] Copying ./cnt_it/cnt_goals_referrer_201205.ibd
to /usr/local/mysql/crontab/cnt_it/backup/innodb/full/2011-06-1 3_10-10-25/cnt_it/cnt_goals_referrer_201205.ibd
[01] …done
./backup.sh: line 109: 12048 give up xtrabackup --defaults-file=$CNF --backup --target-dir=$BACKUP/$ENGINE/full/$day --datadir=$DATADIR

but if we stop the aplications and buckup mysql ,it will do backup successfully

is it a bug ?

any info is great ,thank you !

it is a bug

bug0:02.26 kblockd/0 41 root 10 -5 0 0 0 S 0.0 0.0 0:04.94 kblockd/1 42 root 14 -5 0 0 0 S 0.0 0.0 0:00.00 kacpid