Fritz,
Sorry for the delay on this. We've done some investigation on the Open Graph issue you're having and believe we've found the issue. Right now, if you have the "Automatically use beginning of article for description" setting enabled, then {SCOpenGraph description=...} tags are ignored on the page.
We're actually working on a completely new Open Graph implementation that will be released with the v4.3 release of JFBConnect (within about a month). That will have a lot more flexibility in how Open Graph tags are set both at the article and category level as well as support for more extensions than just Content and K2. Until then, unfortunately, the best I can suggest is disabling the Auto-description and manually setting your own. If you don't set one, the standard meta description tag will be used for the Open Graph description tag as well, so as long as you're setting normal meta description tags, then you probably don't need the auto-description feature.
Hope that helps explain, and sorry for the delay in getting back to this.
Thanks,
Alex