This error has been driving me nuts. We have a server running Apache and Tomcat, serving multiple different sites. Normally the server runs fine, but sometimes an error happ
It may be not a caching issue at all. Try to increase MaxClients parameter in apache2.conf. If it is too low (150 by default?), Apache starts to queue requests. When it decides to serve queued request via mod_proxy it pulls out a wrong page (or may be it is just stressed doing all the queuing).