Same issue here. When I viewed my homepage source I saw this message in the comments...
<!-- This site is optimized with the Yoast WordPress SEO plugin v1.4.7 - http://yoast.com/wordpress/seo/ -->
<!-- Admin only notice: this page doesn't show a meta description because it doesn't have one, either write it for this page specifically or go into the SEO -> Titles menu and set up a template. -->
Which is not very helpful. Is it saying we need to manually add it to the head? I went to the title menu and couldn't see how or what to set up a template with.