Preparing an incremental backup twice can corrupt data

xtrabackup: This target seems to be already prepared.

xtrabackup: error: applying incremental backup needs target prepared with --apply-log-only.

call mtr.add_suppression("InnoDB: New log files created");

let $basedir=$MYSQLTEST_VARDIR/tmp/backup;

let $incremental_dir1=$MYSQLTEST_VARDIR/tmp/backup_inc1;

let $incremental_dir2=$MYSQLTEST_VARDIR/tmp/backup_inc2;

CREATE TABLE t(i INT) ENGINE INNODB;

INSERT INTO t VALUES(1);

echo # Create full backup , modify table, then create incremental/differential backup;

--disable_result_log

exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --target-dir=$basedir;

--enable_result_log

INSERT INTO t VALUES(2);

exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --target-dir=$incremental_dir1 --incremental-basedir=$basedir;

INSERT INTO t VALUES(3);

exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --target-dir=$incremental_dir2 --incremental-basedir=$basedir;

echo # Prepare full backup, apply incremental one;

exec $XTRABACKUP --prepare --apply-log-only --target-dir=$basedir;

exec $XTRABACKUP --prepare --apply-log-only --target-dir=$basedir --incremental-dir=$incremental_dir1 ;

echo # This time should succeed;

exec $XTRABACKUP --prepare --target-dir=$basedir --incremental-dir=$incremental_dir2 ;

# this returns an error according to test pxb170.sh

--error 1

exec $XTRABACKUP --prepare --target-dir=$basedir --incremental-dir=$incremental_dir2 ;

# Cleanup

drop table t;

rmdir $basedir;

rmdir $incremental_dir1;

rmdir $incremental_dir2;