Verified with PS 5.6.25.

mysql> CREATE TABLE `companies` (
    -> `id` int(11) NOT NULL AUTO_INCREMENT,
    -> `site_id` int(11) NOT NULL,
    -> `name` varchar(255) NOT NULL,
    -> `custom1` varchar(255) DEFAULT NULL,
    -> `custom2` varchar(255) DEFAULT NULL,
    -> `custom3` varchar(255) DEFAULT NULL,
    -> `custom4` varchar(255) DEFAULT NULL,
    -> `custom5` varchar(255) DEFAULT NULL,
    -> `custom6` varchar(255) DEFAULT NULL,
    -> `custom7` varchar(255) DEFAULT NULL,
    -> `custom8` varchar(255) DEFAULT NULL,
    -> `custom9` varchar(255) DEFAULT NULL,
    -> `custom10` varchar(255) DEFAULT NULL,
    -> `created_at` datetime DEFAULT NULL,
    -> `updated_at` datetime DEFAULT NULL,
    -> `custom11` varchar(255) DEFAULT NULL,
    -> `custom12` varchar(255) DEFAULT NULL,
    -> `custom13` varchar(255) DEFAULT NULL,
    -> `custom14` varchar(255) DEFAULT NULL,
    -> `custom15` varchar(255) DEFAULT NULL,
    -> `custom16` varchar(255) DEFAULT NULL,
    -> `custom17` varchar(255) DEFAULT NULL,
    -> `custom18` varchar(255) DEFAULT NULL,
    -> `custom19` varchar(255) DEFAULT NULL,
    -> `custom20` varchar(255) DEFAULT NULL,
    -> `custom21` varchar(255) DEFAULT NULL,
    -> `custom22` varchar(255) DEFAULT NULL,
    -> `custom23` varchar(255) DEFAULT NULL,
    -> `custom24` varchar(255) DEFAULT NULL,
    -> `custom25` varchar(255) DEFAULT NULL,
    -> `ticket_count` mediumint(8) unsigned DEFAULT NULL,
    -> PRIMARY KEY (`id`)
    -> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO companies (id) VALUES (NULL);
Query OK, 1 row affected, 2 warnings (0.01 sec)

mysql> INSERT INTO companies (id) VALUES (NULL);
Query OK, 1 row affected, 2 warnings (0.01 sec)
....


# User@Host: root[root] @ localhost []  Id:    50
# Schema:   Last_errno: 0  Killed: 0
# Query_time: 0.000195  Lock_time: 0.000092  Rows_sent: 5  Rows_examined: 5  Rows_affected: 0
# Bytes_sent: 2168
SET timestamp=1441176328;
SELECT companies.* FROM test.companies WHERE companies.id IN (1,2, 3, 4, 5);

After run pt-osc, 

root@desktop:/var/lib/mysql# pt-online-schema-change --nocheck-replication-filters --execute --chunk-size-limit=0 --max-load Threads_running=50 --critical-load Threads_running=500 --alter "ADD COLUMN label_array text" u=root,p=root,D=test,t=companies
No slaves found.  See --recursion-method if host desktop has slaves.
Not checking slave lag because no slaves were found and --check-slave-lag was not specified.
Operation, tries, wait:
  copy_rows, 10, 0.25
  create_triggers, 10, 1
  drop_triggers, 10, 1
  swap_tables, 10, 1
  update_foreign_keys, 10, 1
Altering `test`.`companies`...
Creating new table...
Created new table test._companies_new OK.
Altering new table...
Altered `test`.`_companies_new` OK.
2015-09-02T12:15:28 Creating triggers...
2015-09-02T12:15:28 Created triggers OK.
2015-09-02T12:15:28 Copying approximately 57 rows...
2015-09-02T12:15:28 Copied rows OK.
2015-09-02T12:15:28 Swapping tables...
2015-09-02T12:15:28 Swapped original and new tables OK.
2015-09-02T12:15:28 Dropping old table...
2015-09-02T12:15:28 Dropped old table `test`.`_companies_old` OK.
2015-09-02T12:15:28 Dropping triggers...
2015-09-02T12:15:28 Dropped triggers OK.
Successfully altered `test`.`companies`.

# User@Host: root[root] @ localhost []  Id:    53
# Schema:   Last_errno: 0  Killed: 0
# Query_time: 0.000394  Lock_time: 0.000233  Rows_sent: 5  Rows_examined: 57  Rows_affected: 0
# Bytes_sent: 2243
SET timestamp=1441176328;
SELECT companies.* FROM test.companies WHERE companies.id IN (1,2, 3, 4, 5);