Extra characters appear at the end of the subject heading when replying emails

hi,

i have a very stupid question to asked and this may have been asked before in this forum.

i have a user who gets some additional characters added to the end of a subject heading whenever she replies to her email.

eg. Subject Re: Your Helpdesk Request XXXXXXXX has been registered.362AAB0DFABEE2964825721A00392884

(the additional characters are found after … registered.)

hope some advice can be provided