This is best demonstrated when we just try to request a single CSS file from our IIS server. Sometimes we get the whole uncompressed file back. We'll wait 5 seconds and refresh, then the CSS file is gzipped, 1/5 the original size (which is what we want)... but if we wait another minute, it'll be back to it's original uncompressed version again.
Any ideas what could cause this or how to troubleshoot it?