PageFilter works on http but not https

[sidefx79]

I'm using a page filter to exclude a part of my site from RequestReduce processing as follows:

Registry.AddFilter(new PageFilter(x => x.HttpRequest.RawUrl.ToLower().Contains("/myzone/")));

But while this works fine when I access the site over http it still seems to serve "Reduced" content when access over https. Have I missed something obvious here?