Anomalous reputation scoring behavior

Question

A day or so ago, my achievents icon showed an upvote of 10 rep, and when I clicked on the icon it sent me to:

https://electronics.stackexchange.com/a/195369/43191

it showed the upvote, and after looking over the answer I founed an error, fixed it, and made the answer a little better, in my opinion, by fleshing it out more thoroughly.

Others seemed to disagree, without comment, and after that I received enough downvotes to get me to -1 on the answer page (two, as shown on my user page) and a loss of 12 rep as shown on my achievements icon.

from:

https://stackoverflow.com/help/whats-reputation

I get:

You gain reputation when:

question is voted up: +5
answer is voted up: +10
answer is marked “accepted”: +15 (+2 to acceptor)
suggested edit is accepted: +2 (up to +1000 total per user)
bounty awarded to your answer: + full bounty amount
one of your answers is awarded a bounty automatically: + half of the bounty amount (see more details about how bounties work)
site association bonus: +100 on each site (awarded a maximum of one time per site)

You lose reputation when:
your question is voted down: −2
your answer is voted down: −2
you vote down an answer: −1
you place a bounty on a question: − full bounty amount
one of your posts receives 6 spam or offensive flags: −100

My question is: If I started out with 10 and lost two, I should be left with 8, according to the rules, so how could I wind up with minus 12?

Answer 1

You can see the chain of events under the reputation tab under your profile:

Your edit was at 07:26 which would have bumped it on the front page and 25 minutes later it received a downvote. Then the person that originally upvoted it has removed their vote, it must have been two different people because otherwise the events would be shown at the same time. It isn't possible for one person to downvote an answer and then remove their upvote later.

So for the question:

My question is: If I started out with 10 and lost two, I should be left with 8, according to the rules, so how could I wind up with minus 12?

You got a -2 for the downvote from one person, and the +10 you got from the original upvoter was reverted so you got -10 at that point. Although overall your reputation would only be -2 because essentially it was as though you never received the upvote.

Answer 2

Here is what happened:

1. A user upvoted for a gain of +10. You are now at +10 rep, +1 votes.

2. The same user changed his earlier upvote to a downvote. That cancels the original +10 and adds a -2, for a total gain of -12. You are now at -2 rep, -1 votes.

Users are allowed to undo and reverse a vote for a while. After that, the vote is frozen. However, edits to the question allow votes to be changed again. Your edit bumped the question to the top of the list, and for whatever reason the original upvoter changed his mind, cancelled the upvote and cast a downvote.

No, I had nothing to do with any of these actions.