server type=detail and detail.work file

Hello, I'm starting to play with a virtual server of type = detail. I'm using FR 2.1.12 and the detail server writes to a MySQl DB. I have a stable configuration that just works! I noticed a strange behaviour. If I stop FR, the server leaves the detail.work file, and at the next start FR reloads this file and pushes duplicate records to the DB. Is it a normal behaviour or I'm doing something wrong? Thanks, Andrea