Once you open a file on the server, it can be hard to close the file if there are any file references or relationships to the file. I had a situation like this a couple of years ago. I believe I used a second file to make the connection to the server so when I closed the second file it also closed the file on the server. You can also sometimes avoid using a file reference by using the Open URL set.
Thanks I'm going to try using a 2nd file which has references to the main file and open this using Open URL - would be great if we could explicitly close a file when we know we're no longer going to require that for the session and would be happy for the file to be opened if required down the track.