FCP losing render files
 

On a timeline that is rendered, after we make a change to a clip, the clip then shows it needs to be rendered. We highlight the clip, and choose Render Selection Both (cmd+R). What happens is the selected clip gets rendered but everything else now needs rendering. We haven't had this happen before; any thoughts on what is going on? Thanks.

FCP 6, HDV timeline (all video matches sequence settings), some jpgs on the timeline.