Again ;_;

Well, different people's vote contribute differently to the contribution of upvoted/downvoted person. It depends on rating (yes, CF rating) of voting person. So if you have clean account with single comment and I upvote it, but tourist downvotes it, you get negative contribution.

I'm not so sure about the point raised by BekzhanKassenov but I do know that downvotes on comments aren't displayed until they hit -5, to prevent herd voting / bandwagon effect. They will, however, still affect your reputation.

It's very possible that your first comment got -4 and your second comment got +1, so the net result is still negative.