Content coming from a web application sometimes randomly shuffled

Question

We develop a Java web application which is run on Tomcat. It's been installed on many computers and it's working without problems. Recently, on a single remote installation, it exhibits very strange behavior: Sometimes content coming through HTTP to the browser is randomly shuffled - wrong data being served for a given URL. Most often it manifests as images being randomly exchanged on a web page. But it's not limited to images, it happened to me that instead of a HTML page the browser got one of the images instead.

I tried to debug the problem using FireBug + NetExport, and so far I gathered:

• It appears randomly. Most of the time content is error-free, the problem occurs only from time to time.
• The same application runs on many installations, but only this single installation produces the error.
• It's not connected to a particular browser - we tried different browsers from different computers and the problem persists.
• It occurs when viewed from the server itself (localhost) too, which rules out some broken transparent proxy on the way.
• Both images and HTML pages are affected.
• If wrong content is received, the data itself is consistent: Content-Length, Content-Type, ETags, etc. - everything matches the content. Just that it's wrong data for a given URL.

I'm truly puzzled, I've never seen such an error. I'd be grateful for any ideas how to investigate the problem further.