The Mystery of the Phantom rep [duplicate]

Question

Here's a good Halloween mystery for you. On Tuesday morning I saw a spooky apparition...the vague, spectral shape of 15 rep points off in the distance in a dark corner, that vanished before my eyes as I approached to get a closer look--without leaving a trace!

Despite its rapid dissolution into nothingness, I managed to snap a picture of it, and I'm hoping some paranormal investigator (or maybe a mod) can explain how it is that I have a picture proving that it was not my imagination, despite the total lack of physical evidence.

Here's the ghost story: When I first looked at SO on Tuesday morning, I saw this banner at the top of a previously open tab:

My rep had been at 2,580 just before I went to bed the night before, so naturally, I figured an answer must have been accepted. However, the very next SO page I looked at (I don't recall what, just some other page) showed that the rep was back down to 2,580. I figured there must have been an accept/unaccept. I took a look at my profile to find out which answer so I could see if it required further attention. To my utter befuddlement, the profile not only showed no record of an accept/unaccept, it showed no reputation changes at all for the day:

I'm on Eastern Standard Time, so when I went to bed with the rep at 2,580, it was already about 6 hours into this zero-change day (which remains at zero, with no indication of any changes at all).

After reading "https://meta.stackexchange.com/questions/111373/where-did-this-mysterious-10-reputation-come-from", I checked out https://stackoverflow.com/reputation, but it shed no light on this eerie enigma:

BTW, in case anyone jumps to assume that any question having to do with lost rep is a complaint or a lament, I want to be clear: This isn't "hey, no fair, I want my rep back, boo-hoo!" I don't necessarily know that there was ever any reason for the rep to have gone up in the first place, since it appeared as mysteriously as it disappeared, and no clues were left behind. But I'm the curious sort and I like to understand how things work, especially if I see something that seems out of whack. If I were a cat I'd be dead. (Unless I had black fur, in which case this would be my big night.)

So, what happened? It it possible for someone to accept/unaccept fast enough that it doesn't leave any record? And if so, why would I see the rep change in the banner? Or did I just see the ghost of an accepted answer long deceased that rose from the dead to practice haunting in preparation for tonight?

Answer 1

When an answer is accepted, your reputation is immediately increased by 15 points.

However, if that answer is immediately un-accepted, the event doesn't actually record. This is similar to how if you downvote a question, then immediately un-downvote, your rep does decrease by 1 temporarily, but it doesn't show both the downvote and undownvote event.

I believe you are correct in your supposition that an answer was accepted, then promptly un-accepted. The accept pushed your rep up +15, but before the timeout, it was un-accepted, pushing your actual rep down by 15. Since the global rep counter doesn't show negative rep changes, your screen stayed at 2595 when it should have been 2580.