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!
You're correct, John deliberately changed this as he thought it was a bug. I'll chat to some people to work out what the desired behaviour is.
Previous behavior was chosen intentionally, see this thread for the discussion. I think the change should be reverted.