This is kind of minor, but it seems that the revision history of a post occasionally fails to be written in chronological order, when events are in close succession. For example this post history has an unlocking followed by a locking, when (I assume) the reverse is what really happened.
We could be a little more descriptive in the post history table when it comes to these edge cases, it's just that they rarely come up and get noticed.
Here's the chain of events:
- 5 Close votes accumulate, 4 sending it to math.stackexchange
- Post is closed and locked for migration
- Problem with tags not existing on the destination site, migration rejected
- Post unlocked, closed as off topic instead
What you noticed is an artifact of automatic rejection not taking place until the post is actually locked and all packaged up to go to the destination, which is pretty much by design, since most migrations aren't automatically rejected due to tags. It's a last minute sanity check more than anything.
Whenever you see this, and it all happened in the same second (sometimes seemingly in reverse order), this is almost always the case.
Sorry about the confusion :)