Thank you for your response . I've read the discussions about Truecrypt on this forum, but I could not find a similar case. Maybe I've not been clear enough explaining the issue. As you can read in my post, some synchronization on the encrypted container is done by BTSync. As BTSync is able to detect a change to the volume (changed timestamp), it starts syncing (a part of?) the file. The syncing doesn't take very long. After the syncing is done (no more data transfer at all!), the History tab states 'Updated file personal.tc'. This suggests that there was some form of synchronization. But when I open both volumes on the source and on the target machine, the files are still different (target doesn't contain the last changes). In my opinion it doesn't matter if BTSync tries to sync the whole file after a change or just a small part of it, as long as I can be sure that files get synced by BTSync. Being able to synchronize parts of files is a very nice feature, as long as I can trust the program to synchronize all files correctly (no matter what size or type, Truecrypt or no Truecrypt).