Thanks for finding that!

As far as I can tell, the reasoning is flawed, which is good, since I was concerned there was a better reason for the change that I wasn't aware of. It seems to ignore the inherent difficulty of countervoting a vote that is cast at the beginning of the last 12 hours, because someone finding that the post has been upvoted a couple of horus after the 12 hour period begins is at a serious disadvantage to the initial voter. The change that was made clearly favors the initial voter (either up or down) over later voters.

IMO, the original behavior was better as it favors the distribution of the reward pool over more posts rather than less posts (because it favors downvoting over upvoting) and it served as a better mechanism against abusive voting by large stakeholders to enrich themselves.