Facebook is seeing HTTP code 206 "Partial Content" instead of normal 200 "OK".
206 "Partial Content": This message might occur if a client has a
partial copy of content in its cache and requests and update of missing
content. This message indicates that the partial request succeeded.
I found one old forum post about it: http://forum.developers.facebook.net/viewtopic.php?id=68440
It looks like it might be a server configuration issue to do with caching. Do you run Varnish or anything like that on your server? Check in to that.
Another thing to try might be to move your charset meta tag below your Open Graph tags, so Facebook knows the right encoding to parse them with. Also, using this type tag might work better:
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
Finally, make sure you don't have anything blocking the Facebook scraper user agent. As mentioned in their documentation:
Our bot functions with the User Agent "facebookexternalhit/*". Make
sure you're not blocking that user agent. Also, make sure Facebook's
servers can reach your server.