When I was made a building and logged off, players of the realms asked when it was going to be done. I came back online and saw that half of the building went back about an hour. I re-built that side and tested to make sure it was working, and logged off. People then told me it wasn't working again. Sure enough, it went back to the old way.

It's especially strange because I started working on that side first, so it wasn't the whole world that went back to a previous save. (And I am positive no players would be able to play a prank on me.)

The screenshots are examples of how the shop looked before I logged off, and how it looked after with one side going back to a previous time.