[otrs] merging tickets leaves old ticket

Hello, When I merge one ticket into the other, the old ticket is changed to: (for example) Merged Ticket 2008102110000024 to 2008102110000015. OTRS version is 2.3.2. Is this normal behavior? I have used OTRS in the past, and then it didn't leave any trace of the old ticket after a merge. (except of course in the new ticket) If this can be turned off, how does that work? Kind regards, Amedee