[otrs] Subject some times it has ticket number, some times it doesnt

Hi guys I am testing OTRS 5.0.27. All is running ok, however I found the subject some times it has the ticket number, some times it does not in the received automatic notification. As you can see in the atached image, 3 tickets have ticket number but 1 (the last one) does not. Any ideas about the solution? Thanks a lot. Karlos