I made a quick test in deploying a Vaadin application on Google AppEngine; the application works well but the user interface is mingled. I use a TabSheet component with only one tag.
See the application here:
http://vaadin-cloud.appspot.com/ to understand what I mean.
Works well at least on Chrome 8.0.552.200 (beta channel).
What you are seeing looks very much like a browser cache issue, try clearing your Chrome cache and reloading the page. Maybe you have had there a theme from some earlier Vaadin version, and GAE does not correctly communicate expiration timestamp for it or something like that, so Chrome is using the old version.