You know that often, Google Webmaster Tools shows an image preview of your site's home page on the dashboard listing view of your site profiles within Google Webmaster Tools.
What if the image of your site is wrong? Should you be concerned? Google's John Mueller implies it is really not something to be too concerned about.
In a Google Webmaster Help thread, one person was concerned because his mobile site was displayed in the preview and not his main site. John said, don't "give too much weight to these preview images."
I wouldn't give too much weight to these preview images -- they're not meant to be a representation of how Googlebot crawls the page. If you do see something wrong there, I'd still follow up to see where it came from, but it's not something that would be affecting how we index & rank your website. From what I can tell here, we do recognize your website appropriately, and can pick up the smartphone version. Since the homepage has a very different response size depending on the version that you serve, one way to dig into the details could be to check your server logs, comparing size with the user-agent that made the request, to double-check that your real users get the correct version.
These previews don't represent what Googlebot crawls or your indexing and ranking. It is likely just a style thing for Webmaster Tools.
While the preview for this site looks fine:
My corporate site has a CSS slider image feature which makes the preview for that site look all weird:
Forum discussion at Google Webmaster Help.