Extra line breaks and paragraph breaks in posts

I don't know if this is something occurring because of theme upgrades or not, but it's happening a lot. When we create a post, especially with images, extra line breaks and paragraph breaks will be inserted. If we remove them in HTML mode, they come back when we try to edit the post again later. Very frustrating.

Over on wordpress.com, I see some people having this problem with certain themes, so I'm wondering if this might be a theme-related issue or maybe tied to changes in Wordpress.