It looks like the same bug has caused the monthly reputation league page to show incorrect numbers for the reputation earned this month. (I came across this because I happened to be scrolling through the page just as the UTC day was rolling over. I was going to post this as a new question, but as I explain below, I believe that this is an instance of the same bug reported here.)
As you can see, after I reloaded the page at 0:00 UTC today (when the page updates), there are several users (circled in red) that have apparently earned much more reputation this month than they actually have. Ordinarily, this isn't an extraordinary occurrence: the reputation change per time period displayed in the right column excludes reputation changes from "private" reputation events such as post deletions, so it's not uncommon to see cases from time to time where the reputation change is "higher" than the current reputation.
The oddity here is not merely that - it's the fact that all of a sudden, many users' reputation change this month increased drastically from what they were the previous day. In particular, the user depicted below as being in the #9 position was actually in the #1 position yesterday, with a similar amount of reputation change.
After some research, I determined that all the affected users had answered the now-deleted question, earned a very high score on their answers, and then had their answers erased as a result of the question's deletion. (The user in the #9 spot, whose right column hasn't really changed, had also posted an answer there, but their answer was deleted before the whole question was deleted.)
Additionally, I noticed that you (Makoto) were also one of the users whose rank also suddenly ballooned. Your right column was around 3,000 yesterday, but has risen by around 8,000 to 11,000. Coincidence? I think not.
In summary, while this overall bug may just seem like a minor accounting mistake in reputation history pages, it also affects the reputation league pages, giving people a highly inflated ranking.