I expect all commonly used HTTP clients (Chrome, Firefox, IE, even libcurl) and servers (Apache, Nginx, does IIS still exist?) get this right.

I, too, would expect that the most common pieces of software with massive amounts of engineering time invested get it right (but almost certainly with a performance hit). But I'd be unsurprised to find that one doesn't handle the http parsing spec correctly somewhere.

The issue is that such a spec is entirely unneeded and overly complicated. No benefit, only downsides. And for something as simple as basic parsing rules! Not even getting into anything that should be difficult.