1) Create a new "Content object state group" and name it "go_001".
2) Into "go_001", create two states: "locked" and "not_locked".
3) Change the states in some of your content to "locked".
4) Execute the cronjob

php ezpublish/console ezpublish:legacy:script runcronjobs.php unlock
Running script 'runcronjobs.php' in eZ Publish legacy context
Using siteaccess for cronjob
Running cronjob part 'unlock'
Running cronjobs/unlock.php at: 17/08/2016 12:55 pm
Fetching objects with status : "locked"
Removing lock of eZ Mountains ... Success
Removing lock of Mount Ventoux ... Success
Removing lock of Mount Castor ... Success
Done
Completing cronjobs/unlock.php at: 17/08/2016 12:55 pm
Elapsed time: 00:00:00

The cronjob assumed my User defined Object State as the default locked state and tried to handle it. The query of the cronjob should make sure only the default group would be considered for locks or this limitation should be described in the User defined Object States documentation page

UPDATE ezcobj_state_link
SET contentobject_state_id = 1
WHERE contentobject_id =contentObjectID
AND ezcobj_state.group_id = 2   /*modified*/
AND  contentobject_state_id = 2';