We have Apache 2.2 running on Windows 2k3 and 2k8 R2 as a reverse proxy to downstream applications. Some of these applications may go offline during off-peak hours so we've implemented a custom 503 page like so:

ErrorDocument 503 /error/serverTimeout.html
ErrorDocument 504 /error/serverTimeout.html

(the error directory is in Apaches's htdocs folder)

If I make these changes, restart apache and then access the down application on firefox I see the custom page as expected. I then access it using my IE browser, it also works. If I close my IE browser and access it again, I get Apache's standard "Service Temporarily Unavailable" message instead of my custom page.

Once I receive the standard error message, I never get the custom page again until I restart Apache.

I've put the server on debug and I can't see any difference between the requests which return the custom error page and the requests which return the standard error message.

Is there some weird proxy setting which is messing with the errordocument configuration?

Any ideas?