Hmm, the test fails with Chrome, Edge, Firefox, and Safari.

Yeah, it's true nobody passes the test right now. However, we thought it was best to keep the spec as-is, because nobody submits disconnected forms to the server, and it makes no sense to fire a submit event if you're later not going to submit the form.

In other words, it is better to abort before firing the submit event, if you are disconnected, instead of waiting until after.

>  it makes no sense to fire a submit event if you're later not going to submit the form.

I agree.  We already counted disconnected form submission, and it's very low.  The behavior change should be ok.

https://bugs.chromium.org/p/chromium/issues/detail?id=586749#c10

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cad664141c2aed77dd0049928c1c9d004cce72a0

commit cad664141c2aed77dd0049928c1c9d004cce72a0
Author: shanmuga.m <shanmuga.m@samsung.com>
Date: Wed May 24 23:40:29 2017

Clicking a button on disconnected form should not fire submit event.

Add a isConnected() check in HTMLFormElement::PrepareForSubmission
to avoid firing the submit events.

BUG= 723004 

Review-Url: https://codereview.chromium.org/2900943002
Cr-Commit-Position: refs/heads/master@{#474476}

[modify] https://crrev.com/cad664141c2aed77dd0049928c1c9d004cce72a0/third_party/WebKit/LayoutTests/external/wpt/dom/events/Event-dispatch-click-expected.txt
[delete] https://crrev.com/a0646d775e805babb8d6949f955071011df709f2/third_party/WebKit/LayoutTests/external/wpt/html/semantics/forms/the-button-element/button-click-submits-expected.txt
[modify] https://crrev.com/cad664141c2aed77dd0049928c1c9d004cce72a0/third_party/WebKit/Source/core/html/HTMLFormElement.cpp

I filed a related specification issue.
https://github.com/whatwg/html/issues/2708