xtrabackup prints warnings for tables, not included into partial backup

When preparing partial backup xtrabackup prints warnings for tables, not including into it:

InnoDB: Table db2/t1 in the InnoDB data dictionary has tablespace id 8, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.

How to repeat.

1. Start MTR as:

./mtr --start innodb --mysqld=--innodb_file_per_table=1 &

2. Connect to it and create few tables and databases:

use test;
create table t1(f1 int)engine=innodb;
insert into t1 values(1);
create database db1;
use db1;
create table t1(f1 int)engine=innodb;
insert into t1 values(1);
create database db2;
use db2;
create table t1(f1 int)engine=innodb;
insert into t1 values(1);

3. Make partial backup:

~/build/xtrabackup/bin/xtrabackup --backup --datadir=/home/sveta/build/ps-5.6/mysql-test/var/mysqld.1/data --target-dir=$HOME/BACKUPDIR/issue54226 --databases=db1 --innodb_log_file_size=5242880

4. Prepare it, observe extra warnings:

sveta@linux-85fm:~/build/ps-5.6/mysql-test> ~/build/xtrabackup/bin/xtrabackup --target-dir=$HOME/BACKUPDIR/issue54226 --databases=db1 --innodb_log_file_size=5242880 --prepare --export
/home/sveta/build/xtrabackup/bin/xtrabackup version 2.2.10 based on MySQL server 5.6.22 Linux (x86_64) (revision id: )
xtrabackup: auto-enabling --innodb-file-per-table due to the --export option
xtrabackup: cd to /home/sveta/BACKUPDIR/issue54226
xtrabackup: This target seems to be not prepared yet.
xtrabackup: xtrabackup_logfile detected: size=2097152, start_lsn=(1646642)
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup: innodb_data_home_dir = ./
xtrabackup: innodb_data_file_path = ibdata1:10M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 1
xtrabackup: innodb_log_file_size = 2097152
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup: innodb_data_home_dir = ./
xtrabackup: innodb_data_file_path = ibdata1:10M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 1
xtrabackup: innodb_log_file_size = 2097152
xtrabackup: Starting InnoDB instance for recovery.
xtrabackup: Using 104857600 bytes for buffer pool (set by --use-memory parameter)
InnoDB: Using atomics to ref count buffer pool pages
InnoDB: The InnoDB memory heap is disabled
InnoDB: Mutexes and rw_locks use GCC atomic builtins
InnoDB: Memory barrier is not used
InnoDB: Compressed tables use zlib 1.2.8
InnoDB: Using CPU crc32 instructions
InnoDB: Initializing buffer pool, size = 100.0M
InnoDB: Completed initialization of buffer pool
InnoDB: Highest supported file format is Barracuda.
InnoDB: The log sequence numbers 1625977 and 1625977 in ibdata files do not match the log sequence number 1646642 in the ib_logfiles!
InnoDB: Database was not shutdown normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages
InnoDB: from the doublewrite buffer...
InnoDB: Table db2/t1 in the InnoDB data dictionary has tablespace id 8, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
InnoDB: Table mysql/innodb_index_stats in the InnoDB data dictionary has tablespace id 2, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
InnoDB: Table mysql/innodb_table_stats in the InnoDB data dictionary has tablespace id 1, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
InnoDB: Table mysql/slave_master_info in the InnoDB data dictionary has tablespace id 4, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
InnoDB: Table mysql/slave_relay_log_info in the InnoDB data dictionary has tablespace id 3, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
InnoDB: Table mysql/slave_worker_info in the InnoDB data dictionary has tablespace id 5, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
InnoDB: Table test/t1 in the InnoDB data dictionary has tablespace id 6, but tablespace with that id or name does not exist. Have you deleted or moved .ibd files? This may also be a table created with CREATE TEMPORARY TABLE whose .ibd and .frm files MySQL automatically removed, but the table still exists in the InnoDB internal data dictionary.
InnoDB: It will be removed from the data dictionary.
InnoDB: Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
InnoDB: for how to resolve the issue.
InnoDB: 128 rollback segment(s) are active.
InnoDB: Waiting for purge to start
InnoDB: 5.6.22 started; log sequence number 1646642
xtrabackup: export option is specified.
xtrabackup: export metadata of table 'db1/t1' to file `./db1/t1.exp` (1 indexes)
xtrabackup: name=GEN_CLUST_INDEX, id.low=23, page=3

[notice (again)]
  If you use binary log and don't use any hack of group commit,
  the binary log position seems to be:

xtrabackup: starting shutdown with innodb_fast_shutdown = 0
InnoDB: FTS optimize thread exiting.
InnoDB: Starting shutdown...
InnoDB: Shutdown completed; log sequence number 1655621

Suggested fix: suppress these extra warnings.