You're right, it has been noticed before. It's a little wrinkle in whatever calculation is used that seems to insist on odd numbers of karma being given...or even...or something...I can never remember. I'd go looking for the details of the idiosyncrasy, but it looks like you all might enjoy trying to figure it out again.
Let us know when you do. It's not likely going to change, but at least we'll have rediscovered something about MR KarmaMaths (or KarmaMath for my US friends).
Marc (To the square root of -1 and beyond!)