I am already using a tool like that, but even specifying meta's for facebook won't change the behaviour. Also installed the suggested plugin and there was no difference.
Using firebug I can see the flare bar in HTML, but although it's hidden via CSS (I am not displaying a flare bar at the top of a post) the text is pulled in. I guess it could be fixed by removing the HTML for invisible Flare bars, but there mus be another way?
My fb page displays several of the described cases when I post a link to a specific blog post such as this one: http://www.beatrixfuhrmannphotography.co.uk/2013/03/07/london-engagement-photos-at-the-southbank-ben-chris/
Thanks for your help.