You may be right about the self-voting thing. I upvote loads of people, including my own comments sometimes, but usually not. Anyway, I fell ill, for a day or to and couldn't participate much on Steemit, so I went and upvoted some of my older comments. It was a bit random, but I thought "Why not? Today I can't give it to anybody else.". Shortly after sadkitten appeared and down-voted a load of my comments. There was no explanation, no warning, no nothing. It could be that.