So last summer I did a refactoring on the HTTP parsing layer. Back then I identified that there's certain parts of RFC that we don't really support. So I introduced this option for proxy mode just in case if somebody will be building smth on top of Cheroot which CherryPy isn't going to support because it's a framework for web server apps, not proxies.
I've made this proxy mode disabled by default in Cheroot but the way CherryPy worked required it to be enabled for backwards compatibility so I've set this value to
True in the WSGI adapter on the CherryPy side.
And it's like this since then. IIRC there was smth with nginx reverse proxying which worked differently but I don't really remember the details.
It's up to you to figure out now :)