It kinda makes sense. I mean, technically you like your own post, otherwise you wouldn't upvote it.
But in practice, it does make sense. If all posts are automatically upvoted, there won't be any taboo or ill feel about users upvoting their own post as everyone does it.
There've been a few occasions where I disagreed with my own post. I couldn't just let myself get away with bs comments, so I had to downvote to teach myself a lesson.