Vanish with Opera

[pub crawler]

Was testing something today in Opera browser (latest) under Ubuntu
9.10.    Requests go through Varnish to our cluster - thus the
relativity.

I can't figure this one out.

If I load a page in Opera like:
http://www.pubcrawler.com/Template/events.cfm

It loads fine. If I hit CTRL-R or reload icon I get:
Error 200 OK

OK
Guru Meditation:

XID: 1003261083

If I hit CTRL-R or reload a second time I get:
Error 503 Service Unavailable

Service Unavailable
Guru Meditation:

XID: 1003261718


Is there something anyone can thing of that would cause this behavior?

Thanks!