Hi Dalsvzla,
I have a similar backup to yours, which I suspect is rare by the way, and the progress indicator does not appear to work. This would be a bug of course, but I am afraid it is one of the lowest priority to fix.
Otherwise, the process does complete and "success" is reported in the 320's web interface and I have verified that the new data is backed up. I have mine set to do an "incremental" backup, scheduled to run at 2:30 AM, so I am not too concerned about the progress indicator. Just that the data is backed up. I doubt that many others have a similar setup so that is why no other responses. Anyway, I am just glad the backup works. Good luck and regards