Not all CGI variables show up using CFDUMP

CGI variables must be something special - it is not possible to show all cgi variables when doing a cfdump. I just came across this bug when trying to use a custom #404 page where apache provides the original page URL in the CGI variable REDIRECT_URL.
I am just using CGI.REDIRECT_URL now and it works.
The interesting thing is that StructKeyExists(CGI, blabla) does not work at all - the check will always return true.