So, I've only recently caved and made my account on Slashdot, and I'm still learning about the karma system. I made a few comments on stories but they weren't on the main page and weren't all that noteworthy so they just sort of sat there with the default point value of 1. Then one day I posted in a story on the main page. In retrospect the post could have been funnier or more informative, but it wasn't bad either.
It was moderated -1, Redundant. This seemed odd because it wasn't redundant, at least not in a literal sense. Nobody else had responded to the post that I was responding to (or at least not in a remotely similar way). But I shrugged and continued. Quickly I discovered that my karma was now, from that single infraction, "Bad" and everything I post is at 0 points. This makes them less visible, which is a little annoying.
A little after that, I saw that I had gained the achievement "Had a Comment Modded Up". My karma was still Bad, so I looked at my posts and found that the only change was that the "redundant" one had been simultaneously modded Overrated and Underrated. It still said it was redundant, and the score was still 0.
A little after that, it changed again - now it has a score of 1 (as it did originally) and is marked "Insightful". My overall karma is still bad, and my posts still default at 0. Since then I've had another modded +1 Insightful and one modded +1 Funny. That means if I look at a list of my posts and exclude those that are at the default, it looks like this:
Score 1, Funny
Score 1, Insightful
Score 1, Insightful
Three positive, no negative... and that's bad karma. To be fair I think one of the insightfuls probably counts as a 0 rather than a 1 because when that one got posted my default was 1... but either way I'm really confused. I'm sure I'll figure it out someday, I feel like Slashdot probably knows what it's doing, but right now this looks insane.