I was at my rep cap (245), and downvoted someone. I therefore had 244 rep. Soon afterward, I got an upvote, putting me back to 245 (thanks to the new rep rules). After that, I removed my downvote, and lo and behold, fellow unicorns: my rep for the day is now 246!
Update, FWIW: after a couple accepts (246 to 276), I downvoted again (276 to 275), and got two more upvotes. This time, however, they didn't give me +1 like the other time. I'm going to try undownvoting to see if it goes back up to 276.
Update 2: Yes, it does go back up to 276. What's weird is that it doesn't either stay at 275 (like it should) or go up to 277 (to be consistent). And my rep profile page still doesn't register the four downvotes/undownvotes.
Update 3: The +1 extra rep has moved to my latest upvote (which dates to after my last undownvote), rather than where it was on an upvote a couple hours ago, for no reason I can make out. Stranger and stranger. I just downvoted again, and went back to 275, waiting for another upvote.
Update 4: OK, no go. The upvote didn't give me +1. So maybe it was a one-time glitch?