IFrame object loads wrong pages !?!?!

This is truly a bug from hell.

For the last two days the upload page on our site behaves very strange. If it was not so creepy i would say the page is sick :-)
this page includes an IFrame object that shows a second page inside, we will call them Outer page and Inner page.
What happends is this: when entering the outer page we sometimes see the inner page correctly. Other times we see the inner page broken, and the source shows that not all page was loaded. Other times we see even stranger things: the inner page is partially loaded and a totally different page is appended to it's end, creating a total mess on the page.

this bug appears only on our production server (dedicated, hosted) and not on our internal network. We tried to move the javascripts on the page around with no change. We tried putting a meta tag that prevents caching of the page - again nothing changed.

We are going to try a sniffer on the response and compare it with the browser source, maybe something goes wrong while rendering this page.

I have not fount any documentation of such a bug anywhere on the net. I still didn't get any answers from any newsgroup or from Experts Exchange (a great technical solution site). I'm getting a little worried...

If anyone ever encountered such a problem or has any suggestions i will be happy to hear it.
I will keep rolling this story as it happends.

Scratching my head :-)
Benny.