Along with the inability to upload images into posts, published posts are occasionally changing the size and/or style of the post font. For example, scroll to the second post, “Changeling”: http://waynemelton.wordpress.com/
And when you paste from an external source other than a simple text editor, or Live Writer, do it via the “Paste as plain text” button, to avoid introducing unwanted font etc. commands. You can do the same to correct your already published posts.