I'm having the same problem. I'm using calibre-server --with-library /path --daemonize --auto-reload and syncing the server library using SSH ftp (not dropbox, so the dropbox issues don't apply to me). I can confirm that the last modified timestamp is being updated on the server, but the running calibre-server process doesn't seem to be updating.
Are other similar setups working properly? Does the server check for updates on a fixed schedule? I can't seem to get the server to update while its running. Thanks for your help.