[otrs] Trouble with ticket number in Subject

Hi there, Using OTRS 4.latest. We have a new installation of OTRS and things seem to be working fine, except that we cannot get a consistent Subject line with a ticket number included. For example, using the standard in the auto-response, it only includes whatever the client sent. ie, not "[Ticket#2015....] Rest of subject..." If I use the following: , then the result is something along these lines: "[Ticket#2015041908000541] 2015041908000541 Rest of subject..." I'm at a bit of a loss. I've compared it to another OTRS setup (also 4.x) which has been operating fine for years (upgraded all the way from 3.whatever), but cannot spot an issue. I'd appreciate any pointers. Thanks Henry