Yoast’s WordPress SEO plugin is not showing the correct snippet [closed]

It is suppose to work this way.
Joost’s plugin only gives you a great tool for you to optimize your snippet.

If you haven’t done any optimizations whatsoever, like creating an awesome brief description of what your content is all about, Google will probably try to figure out what’s the best bit of content by their own.

Just a minor edit, Google just released a video exactly replying your question: http://support.google.com/webmasters/bin/answer.py?hl=en&answer=35624