After the next build was released, a new bug was filed that the browser "Back" button didn't work anymore. MSIE would display an error message about the content being expired (indeed, I'd instrumented the filter to send an HTTP Expires: header) whereas Mozilla (my browser) wasn't quite so facist with the shrill error messages.
The resolution was that the Expires header was ditched. Something else came up with screwy caching behavior and one of my colleagues turned off the filter, declaring that using META HTTP-EQUIV tags in the JSP was the "right" way to fix it. I never got a good explanation as to why that was "right" but as long my old bug wasn't reopened, I didn't lose any sleep over it.
I believe they say, "c'est la vie"