Bizarre intermittent behaviour of panels

Since upgrading to Panels 3 on Drupal 6, we have had this problem.

The site normally loads just fine, but every so often it loads with the panel layout broken. This seems to last for a few seconds (even if you click refresh several times), and then returns to normal.

It's very bizarre, and people from all over have reported this behaviour with our site. Although I have seen this behaviour myself, I am yet to trace it due to it's sporadic nature.

I've attached some screenshots though to illustrate the issue- has anybody any idea where this may be coming from? I thought it could be a caching issue, where for a few second the CSS becomes unavailable, but this is only a theory.

Bad load.jpeg = broken
Screenshot-13.png = normal load

The site itself is available at http://www.wikijob.co.uk

Any help would be much appreciated!

Thanks,
Chris.