That's a bug, though it sounds like a very cool one. The rewind stuff was a bit of a mess to code and I thought I had managed to get it be fairly solid, but it wouldn't surprise me if there's still problems there - I will try to figure out the cause of this one. I had a lot of stuff in mind for interesting puzzles to do with rewind, though not much is in there later. Since a particular item can only exist at one point you take stuff from people just by having it yourself, although that means a lot of special conditions to check for to make things make sense.