On the other hand, my 30-day karma shot up by over 50, independent of my total karma. I'd been puzzling over this, because there's never been a point in time when I had enough downvotes all at once to account for that sort of leap when they passed beyond the 30-day threshold.
It seems that if you look at the column on the right of the page, you can see upvotes and downvotes separately for recent posts. The same [n, m] format is displayed for recent comments, but it doesn't seem to actually sync with the score displaying on the comment. This feature only seems available on the sidebar: looking at the actual comment or post doesn't give you this information.
Thanks, whoever did this!