Thanks for confirmation. But I have no other machines. Anyway, I set up two windows schedules, which are repeated every hour (maybe longer when I don't edit the database much)
1) Kill calibre-server
(wait 5 minutes for all files to be synced automatically)
2) Run calibre-server.
This means that the server is offline 5 minutes every hour,

, but I can live with that.
//
PS: I use Bittorrent Sync, so the sync is quite fast.