Facebook Returns Wrong URL Forwarded Domain

I’m having a few issues with my new imageboard style site. I believe they are related to a forwarded domain. I have a home web server that I initially set up using a dyndns.org address. Then I registered a domain name ‘mydomain.com’ and forwarded it to my ‘dyndns.org’ addy. I also masked it so the users see ‘mydomain.com’.

Now when a user likes a post on my site, facebook displays my ‘dyndns.org’ address rather then ‘mydomain.com’. It also displays the thumbnail to the image.

I I change the site address url in settings to ‘mydomain.com’, facebook returns the correct address, but doesn’t display the associated image thumbnail.

Any help would be appreciated.