In using the default rule set for the VIA header, available from McAfees online list, or here on the site, we are having two issues:
Our current ruleset is attached and only a slightly modified version of McAfees ruleset.
First of all, you only need to run this ruleset in request mode. Other than that, the rules should work. Only thing I could think of is if you have the proxy control setting incorrectly set, that would still append the via header, even despite the other events. Can you share a screenshot of the proxy control setting?