I agree it's not that "nice" when you find someone who comments on a post you've made and then upvotes their own comment but not your post :/
I don't personally agree this is something that should necessarily be punished however. The way this kind of behavior is best moderated from my perspective is through showing that it isn't supported or appreciated behavior socially speaking. I for one will for instance not upvote such a comment or follow someone whom I know does not really support me, or anyone else for that matter.

If they do give support and also support themselves by upvoting their own comments, then I don't see a problem with that.