Client Ref Search Field No Longer Working!?

Previously I have carried out hundreds of searches in the Client Management ‘View Clients’ within the ‘Client Reference’ field to find those customers with a particular set of characters e.g. ‘diary0124’ or ‘diary0224’. However, the field no longer appears to accept field containing what is entered only if the field begins with it. I am not sure why this has changed as it previously worked fine. Is there a reason?
Can you please reverse this back to the way it was originally setup so that if any of the customer ‘client reference’ field contains the text entered it then displays the records. Thank you.