What is the issue with the HTML Standard?

If I loadhttps://www.example.com/ and the TLS certificate says it is only valid forhttps://example.com/ then Chrome and Firefox will openhttps://example.com/ without prompting the user, whereas Safari and cURL both warn about an invalid certificate and fail to load. From examining Chromium source this seems limited to "www" subdomains. Loading an image or iframe fromwww.example.com with such a mismatch shows a failed load, so this seems to be limited to main frame navigations. This seems worth standardizing and aligning behavior on for increased interoperability.