This question already has an answer here:
I read a question, thought it was interesting, voted it up. It needed some editing, so I started fixing all the grammar mistakes, added punctuation, improved sentence structure; I realized that the quality of this question was very low - it felt like the OP didn't put any effort into it at all - no evidence of research was provided, and a very unclear question was asked.
I changed my mind about the upvote, but I couldn't change my vote until the post was edited. In a couple of minutes my edit was accepted, and I was able to change it to a downvote.
Is it normal? It just seems weird that your own edit can let you change your vote on a question.