Intermittent problem loading stylesheets and javascript on extranet

On some extranet pages (every couple of times), I get a page load without javascript or css.

For example, the link to the CSS on this page:

http://extranet.atlassian.com/display/%7Edaniel.hurst@atlassian.com/Specifications?focusedCommentId=500334761#comment-500334761

Is this:
http://extranet.atlassian.com/display/%7Edaniel.hurst@atlassian.com/null/s/638/1/1/_/styles/main-action.css?spaceKey=~daniel.hurst@atlassian.com

A refresh seems to fix it about 50% of the time.

It seems to be that instead of 'request.getContextPath()', we are getting '/display/%7Edaniel.hurst@atlassian.com/null/' instead. Looks like some race condition?