Page These Rending Problem

I'm in the final stages of creating a drupal environment.

I selected and installed the greenthing theme, but when I navigate the site, the response object I often get is immediately an unformated plain vanilla HTML page and then, about a second later, the fully rendered greenthing theme. After a page is cached it stops. Does anyone know what causes this?

You can observe it at www.grahn400.com/drupal

Thanks,