[otrs] ticket hook at subject is repeated

I did recently install the 2.2.5 OTRS version as a demo.   I did set up one queue, two agents, 3 responses.   After an user customer create a ticket sending a mail, OTRS answer with an automatic response and after that an agent answer that ticket with a response; all is ok. But when the user customer reply to ask more information, the automatic response sent by OTRS show the subject repeated as follows:   "Re: [TktDemo#200809084002] [TktDemo#20080908400 [...]"   So, the next response sent by the agent to the user customer will have the ticket hook repeated instead of the original subject.   How I can avoid the double ticket hook?   Thanks for the help   Karlos