Why is the wrong thumbnail, title or description being posted to Facebook ?
This information (title, description, thumbnail) is selected automatically by the Facebook Graph API, we can't control this ourselves.
However, you can influence this (and tell Facebook what information they should retrieve for posting) by using the Open Graph tags in your content, see e.g.
for a summary of these tags.
There is also a handly Facebook debug page at
, where you can enter a URL that points to a page on your site, and Facebook tell you exactly what information they retrieve from your site when this page/link is shared on Facebook.