This is odd indeed, but easy to reproduce. I discovered it by accident (long story). The bottom line is that after deleting files from the archive, and then emptying the trash, they can mysteriously RAPIDLY reappear in the archive after a backup. Let me explain....
1. Start by doing a manual backup just to get everything up to date.
2. Delete a large file from your archive. Something that would take a noticeable time to back up again. In my case, it was an Outlook .pst file a bit over 1GB.
3. Go to the Trash and "delete the trash file permanently". Verify, using both the iDrive app and the web interface, that the file is gone and that the Trash is empty. It's really gone now, right? (...but just wait!)
4. Run a manual backup again. The backup operation will quickly complete (i.e., in the normal amount of time it would take to scan through all the files in your backup set). In my case, that's about 5 minutes, but it would have taken more than an hour to actually push the 1GB file up to the archive from scratch.
5. Note that in the backup log, it will say "Files backed up now: 0" - so iDrive is saying that it didn't need to back up any files (even though we just deleted one of our files from the archive...hmmm).
6. Now go look in your archive, and VOILA!, the big file that you deleted and purged from Trash has mysteriously reappeared in its proper place.
So somehow, even after deleting a file from my archive and emptying the trash, iDrive has a copy of my file somewhere that it can quickly add back to my archive. Somehow, this makes me a little nervous! So I expanded my experiment (at some risk, but I wanted to know!).
1. I deleted ALL my files from the archive. That was 28,000 files, just over 100GB of data.
2. I "permanently deleted" them from the Trash. Everything looked like it was gone.
3. I ran a manual backup. Guess what - it took just 5 minutes (the normal time to scan through my files), and at the end, iDrive said "Files backed up now: 0", and when I looked online, all my files were magically back in my archive!!!
So, iDrive folks, what the heck is going on here?