NOTE:  not 100% certain this is the exact same bug, but this behavior was detected while trying to duplicate it. Appending note to existing bug per discussion with developer

Able to see a similar failure, but *only* under the following conditions:
1)  7 schemas (all identical).  Each schema has 100 tables,   Tables are 1-100 rows (table1 has 1 row, table 100 has 100 rows)
2)  innodb_file_per_table is enabled
3)  --parallel=50 passed to xtrabackup.

Reducing either the number of schemas or the --parallel value results in a passing test.

However, with this command line:
./dbqp.py --default-server-type=mysql --basedir=/mysql-5.5 --xtrabackup-path=/percona-xtrabackup/mysql-5.5/storage/innobase/xtrabackup/xtrabackup_innodb55 --innobackupex-path=/percona-xtrabackup/innobackupex --suite=xtrabackup_basic bug826632_test

We see this:
20111101-103351  ===============================================================
20111101-103351  TEST NAME                                  [ RESULT ] TIME (ms)
20111101-103351  ===============================================================
20111101-103351  xtrabackup_basic.bug826632_test            [ fail ]    88564
20111101-103351  test_basic1 (bug826632_test.basicTest) ... FAIL
20111101-103351  
20111101-103351  ======================================================================
20111101-103351  FAIL: test_basic1 (bug826632_test.basicTest)
20111101-103351  ----------------------------------------------------------------------
20111101-103351  Traceback (most recent call last):
20111101-103351  File "/dbqp/percona_tests/xtrabackup_basic/bug826632_test.py", line 99, in test_basic1
20111101-103351  self.assertTrue(retcode==0,output)
20111101-103351  AssertionError:
20111101-103351  InnoDB Backup Utility v1.5.1-xtrabackup; Copyright 2003, 2009 Innobase Oy
20111101-103351  and Percona Inc 2009-2011.  All Rights Reserved.
20111101-103351  
20111101-103351  This software is published under
20111101-103351  the GNU GENERAL PUBLIC LICENSE Version 2, June 1991.
20111101-103351  
20111101-103351  IMPORTANT: Please check that the apply-log run completes successfully.
20111101-103351  At the end of a successful apply-log run innobackupex
20111101-103351  prints "completed OK!".
20111101-103351  
20111101-103351  
20111101-103351  
20111101-103351  111101 10:33:51  innobackupex: Starting ibbackup with command: /percona-xtrabackup/mysql-5.5/storage/innobase/xtrabackup/xtrabackup_innodb55 --prepare --target-dir=/dbqp/workdir/bot0/s0/var/_xtrabackup --use-memory=500M
20111101-103351  
20111101-103351  xtrabackup: cd to /dbqp/workdir/bot0/s0/var/_xtrabackup
20111101-103351  xtrabackup: This target seems to be not prepared yet.
20111101-103351  xtrabackup: Temporary instance for recovery is set as followings.
20111101-103351  xtrabackup:   innodb_data_home_dir = ./
20111101-103351  xtrabackup:   innodb_data_file_path = ibdata1:10M:autoextend
20111101-103351  xtrabackup:   innodb_log_group_home_dir = ./
20111101-103351  xtrabackup:   innodb_log_files_in_group = 1
20111101-103351  xtrabackup:   innodb_log_file_size = 2097152
20111101-103351  111101 10:33:51 InnoDB: Using Linux native AIO
20111101-103351  xtrabackup: Starting InnoDB instance for recovery.
20111101-103351  xtrabackup: Using 524288000 bytes for buffer pool (set by --use-memory parameter)
20111101-103351  111101 10:33:51 InnoDB: The InnoDB memory heap is disabled
20111101-103351  111101 10:33:51 InnoDB: Mutexes and rw_locks use GCC atomic builtins
20111101-103351  111101 10:33:51 InnoDB: Compressed tables use zlib 1.2.3
20111101-103351  111101 10:33:51 InnoDB: Using Linux native AIO
20111101-103351  111101 10:33:51 InnoDB: Warning: innodb_file_io_threads is deprecated. Please use innodb_read_io_threads and innodb_write_io_threads instead
20111101-103351  111101 10:33:51 InnoDB: Initializing buffer pool, size = 500.0M
20111101-103351  111101 10:33:51 InnoDB: Completed initialization of buffer pool
20111101-103351  111101 10:33:51 InnoDB: highest supported file format is Barracuda.
20111101-103351  InnoDB: Log scan progressed past the checkpoint lsn 108804860
20111101-103351  111101 10:33:51  InnoDB: Database was not shut down normally!
20111101-103351  InnoDB: Starting crash recovery.
20111101-103351  InnoDB: Reading tablespace information from the .ibd files...
20111101-103351  InnoDB: Error: trying to add tablespace 384 of name './test2/table85_int_autoinc.ibd'
20111101-103351  InnoDB: to the tablespace memory cache, but tablespace
20111101-103351  InnoDB: 384 of name './test2/table84_int_autoinc.ibd' already exists in the tablespace
20111101-103351  InnoDB: memory cache!
20111101-103351  /percona-xtrabackup/mysql-5.5/storage/innobase/xtrabackup/xtrabackup_innodb55 version 1.6.3 for MySQL server 5.5.10 Linux (x86_64) (revision id: undefined)
20111101-103351  xtrabackup: xtrabackup_logfile detected: size=2097152, start_lsn=(108804860)
20111101-103351  innobackupex: Error:
20111101-103351  innobackupex: ibbackup failed at /percona-xtrabackup/innobackupex line 354.
20111101-103351  
20111101-103351  
20111101-103351  ----------------------------------------------------------------------
20111101-103351  Ran 1 test in 88.562s