I have a similar problem with comments on my blog . they are in italian and they use characters with accents like àèìòù.
well, if I add a post from the public area of the blog, they get encoded not the right way which is & egrave ; and so on, but they get encoded as error chars like if they were encoded from another charset into ASCII, just like the example you show above.
But, if I add a comment from within the admin area, they get encoded correctly.