Meta descriptions and facebook

Hi

As much as we love easy blog and how easy it makes everything for us, we are still wondering why the meta descriptions area of easy blob, sometimes shows up on face book and sometimes doesn't.

So we'll input a description of the article in the meta description area, then post to face book, the link some times picks up the meta description and some times doesn't.

Can you explain why please and what we can do to guarantee it does happen.

Thanks

Alex