What is the issue with the HTML Standard?

See step 11.5 of https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-form-submit
this as specced means that a submit button in a dialog form will always override the dialog's returnValue because a button always "has a value" (it's an empty string when missing the value attribute).

However, Chromium and WebKit implement this step as "has a value attribute" which is not the same thing.

I believe Chromium and WebKit implement this as would be expected and the spec should be updated to clarify (with tests added for this case).

Test Case: https://jsfiddle.net/wfhgc9yd/