Media Management - relink to new files?

Hi,
when i using the media mangement, and i choose "used media and trim ... " , the option "relink to new files" is grayed out. Why? I missed something? I need this feature back!
when i using the media mangement, and i choose "used media and trim ... " , the option "relink to new files" is grayed out. Why? I missed something? I need this feature back!