Unexplained Undownvote after 4 days on an unedited post

Question

A few days ago someone serial-downvoted my questions:

It didn't bother me too much, and I let the serial voting script to reverse the downvotes, and it did - Except of one question:

One downvote is not the end of the world, so I just moved on. But today however, I noticed something strange on my reputation summary - An undownvote event on that remaining downvoted question:

I posted that question on Dec 2013 and it has never been edited. I wonder how could this scenario be possible, to undownvote after 4 days since the vote was originally cast. Or maybe it was the leftovers of the voting script that was reversed 3 days later?

I searched for similar questions and come across Serial downvote reversals don't always appear as such but the accepted answer confimed it was a bug that was fixed, so I'm confused by that delayed undownvote.

Answer 1

They didn't retract it. At some point a staff member came by and invalidated the 4th vote that wasn't invalidated with the other three. The system actually isn't that smart when determining if the vote retractions were from a reversal or not.

The current behavior is that if there are multiple vote reversals that all have the exact same timestamp and all came from the same user, they just get grouped together as a "Voting corrected" event. If that user is deleted, it changes to "User was removed". That is a bit of an oversimplification of the logic, but that's really all that happens there.

Since the reversal of the last vote was a solo event with no others around it, the system doesn't group it as a voting correction as you'd normally see.