Setting User-Agent header on the browser has surprising results

ua-quirk.ts

// Chromium bug: https://issues.chromium.org/issues/40450316

const headers = new Headers();
headers.set("user-agent", "fancy/1.0");
console.log(headers.get("user-agent") == null);
// Prints: false

const req = new Request('');
req.headers.set("user-agent", "fancy/1.0");
console.log(req.headers.get("user-agent") == null);
// Prints: true