Non-activated default buttons prevent implicit form submission.

Source/core/html/HTMLButtonElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 141 matching lines @@
     HTMLFormControlElement::defaultEventHandler(event);
 }
 
 bool HTMLButtonElement::willRespondToMouseClickEvents()
 {
     if (!isDisabledFormControl() && form() && (m_type == SUBMIT || m_type == RESET))
         return true;
     return HTMLFormControlElement::willRespondToMouseClickEvents();
 }
 
-bool HTMLButtonElement::isSuccessfulSubmitButton() const
+bool HTMLButtonElement::canBeSuccessfulSubmitButton() const
 {
     // HTML spec says that buttons must have names to be considered successful.

[eseidel, 2013/11/14 16:40:32]

Interesting that we're choosing to follow one bit of HTML5 here, but not
another.

[tkent, 2013/11/15 00:04:31]

It seems the WHATWG specification doesn't ask it.  We should remove the comment.

[sof, 2013/11/15 08:52:15]

Done. I couldn't find any mention of this either (nor could others here remember
this being a constraint at some point.)

     // However, other browsers do not impose this constraint.
-    return m_type == SUBMIT && !isDisabledFormControl();
+    return m_type == SUBMIT;
 }
 
 bool HTMLButtonElement::isActivatedSubmit() const
 {
     return m_isActivatedSubmit;
 }
 
 void HTMLButtonElement::setActivatedSubmit(bool flag)
 {
     m_isActivatedSubmit = flag;
@@ skipping 28 matching lines @@
 {
     return m_type == SUBMIT && HTMLFormControlElement::recalcWillValidate();
 }
 
 bool HTMLButtonElement::isInteractiveContent() const
 {
     return true;
 }
 
 } // namespace