Mobile Google Search Tests Oversized Header

I'm not sure if this is a bug or a new Google experiment, but I've noticed a different mobile search interface that uses more space for the header. There's a Google logo, a search box and a list of specialized search engines below the search box. It's based on the experimental interface I've mentioned in a previous post.

If you enable the search tools and restrict results to a certain date range, the new header uses even more screen real estate.

For some reason, this experimental interface is only used when searching from Google's homepage. Chrome's search box sent me to the compact UI.