Typepad's a bit wonky about comments. A lot of times it'll sit and load for a long time after you hit Post. Just try hitting reload when this hapens and chances are you'll find your comment has been added to the post. Just to be safe, you should highlight the text of your post and hit Copy, so that if it doesn't show up you can Paste it back into the comment box and try posting again. If, while waiting, you hit Post a second time, there's a good chance you'll end up double-posting.
My policy on double-posts is that I'll go through and delete them right away when I see them. There's no need to point it out. I'll also delete any comments telling me "Hey! I double posted!" assuming there's no other content to the comment; that way the comment section doesn't end up with you saying "Hey! I double posted!" but there's no second post anymore because I deleted it. I'm just telling you this so that noone accuses me of censorship or anything. I'm just tending the garden.