Customize Access front end

I have an MS Access database split into front and back ends on a shared network drive. I have copied the front end to end-user's PC desktops. When I open the front end on the shared drive and make changes, the changes show up on the PC copy. Why? I thought I was supposed to be able to customize the front end for each user for their specific needs. And I don't understand why changes on a file sitting on a shared drive results in changes in a file on a local PC. Any advice would be appreciated.