Comment 1 for bug 358195

xtrabackup don't cause new records for insert buffer.
So, we cannot disable insert buffer if the records exist already.

But, in the previous revision, innodb_fast_shutdown is set to 0 (all insert buffer records should be processed before shutdown).
It is not normal value of MySQL/InnoDB. I have changed it to 1.
It was my mistake.

http://bazaar.launchpad.net/~percona-dev/percona-xtrabackup/trunk/revision/41

I think the change may be enough.