[otrs] Removing leading zero from ticket number

We have a ticket numbering system of type 'Year', e.g. 2014-xxxxx. Now, after having created 9999 tickets, the ticket number went from 2014-09999 to 2014-010000. We really want to get rid of the leading zero but have no clue as to why the leading zero is added. The minimum length is 5, which has been reached. The TicketCounter.log does not contain a leading zero. If anyone can give me a quick hint... it would be appreciated! Regards, Sander