The repeat seems to be a OSX/Yosemite bug that some have seen, and is often fixed by a reboot. If you open the display preferences does the thumbnail change correctly?
Second, I'm seeing this bug and yes, in the Desktop & Screen Saver settings, the thumbnail is correct (you can see what it should be by opening the menu bar dropdown and clicking the title of the piece which will open it in the browser straight from s3).
Edit: tried reboot, the app tried to autostart but crashed. Started it manually, it kept crashing a few times. It is now running but still showing a particular image on every other change, even automatic.
I have submitted an update to Apple, currently pending approval. Hopefully it will be available on the App Store soon and fix the issues you're seeing.
It's interesting that no matter how much one tests, bugs invariably appear for some percentage of users, given the configuration of the software and the environment of the machine. I liken it to manufacturing defects that present at so many sigma. It's because of feedback from users like you that things get better, so thanks for taking the time to comment!
