Pasting link of my homepage to FB wall does not display OpenGraph excerpt, OG meta tags are present

I am currently working on our website, which I am publishing using WordPress and the Yoast WordPress SEO plugin. I have checked the HTML source and the Ope开发者_如何学运维nGraph meta information is present:

screenshot of html source of our site www.verstrickt.at here:

However when I post the link to my wall the only thing it displays is:

screenshot of posted link on FB wall:

Anyone any ideas why this is happening?

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