Consider sync'ing data to disk after copying it to Persistent Storage when activating a feature

This would ensure the UI correctly reflects, via the transitional switch state, whether the data was really copied to disk. In turn, it would decrease the risk that the user reboots while the data is not on disk yet, which in turn reduces the risk of a broken filesystem (in theory I suppose we sync' and umount during shutdown, but this may or may not be reliable).