Non-activated default buttons prevent implicit form submission.

Source/core/html/HTMLInputElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 313 matching lines @@
     virtual void collectStyleForPresentationAttribute(const QualifiedName&, const AtomicString&, MutableStylePropertySet*) OVERRIDE;
     virtual void finishParsingChildren();
 
     virtual void copyNonAttributePropertiesFromElement(const Element&);
 
     virtual void attach(const AttachContext& = AttachContext()) OVERRIDE;
 
     virtual bool appendFormData(FormDataList&, bool) OVERRIDE;
     virtual String resultForDialogSubmit() OVERRIDE;
 
-    virtual bool isSuccessfulSubmitButton() const;
+    virtual bool canBeSuccessfulSubmitButton() const OVERRIDE;
 
     virtual void resetImpl() OVERRIDE;
 
     virtual void* preDispatchEventHandler(Event*);
     virtual void postDispatchEventHandler(Event*, void* dataFromPreDispatch);
 
     virtual bool isURLAttribute(const Attribute&) const OVERRIDE;
     virtual bool isInRange() const;
     virtual bool isOutOfRange() const;
 
@@ skipping 58 matching lines @@
     // that it lives as long as its owning element lives. If we move the loader into
     // the ImageInput object we may delete the loader while this element lives on.
     OwnPtr<HTMLImageLoader> m_imageLoader;
     OwnPtr<ListAttributeTargetObserver> m_listAttributeTargetObserver;
 };
 
 DEFINE_NODE_TYPE_CASTS(HTMLInputElement, hasTagName(HTMLNames::inputTag));
 
 } //namespace
 #endif