So I've been using Retrospect 11.0.1 on Mac OS X 10.8.5. Here's what I've been encountering...
First, I had no clue that you could simply recycle media sets if you were encountering issues with backups -- so rather than recycle them, I "deleted" them altogether and re-created media sets. I figured out a loophole, or so I presume, to maintain my naming conventions on tapes to keep proper organization and so I also don't look like a dingus... my tapes are named as such: 2014 A1, 2014 B1, 2014 C1, and so forth...
So... I took a tape that was already named, SUCCESSFULLY RESTORED it locally, and tried to backup it to a newly named media set and I run into the issue of "No Files Need to be Copied."
Instead of getting a backup of 1.03 TB, I get a backup of 4.5 MBs... or what have you. I've done this multiple times and yielded no success. I'm guessing it's a miscommunication within Retrospect.
Here's a snapshot of the log from the backup.