I want to understand if I did something wrong, or if this is the expected behaviour:
We have had Owncloud in use (8.1.5 back then) and for reasons not really relevant, we had to restore a one week old backup of Owncloud and its data.
We thought this was not that problematic as the clients should push missing files to the server again. But to our surprise it was the other way around, the clients started to also DELETE those files.
I can guess this is a hard to solve problem. But I think it would be good if this was not the way the clients behave.
Obviously the client remembers that the files once were on the server, and are missing now, so it deletes them. But maybe it should also save some kind of counter with each file, and if the counter returned by Owncloud is smaller than the saved counter, it instead assumes that the Owncloud was restored from a backup.
It was the official Owncloud client.