Cousins may not share style when ascendant affected bits set.

third_party/WebKit/Source/core/css/SelectorChecker.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 816 matching lines @@
         break;
     case CSSSelector::PseudoAutofill:
         return element.isFormControlElement() && toHTMLFormControlElement(element).isAutofilled();
     case CSSSelector::PseudoAnyLink:
     case CSSSelector::PseudoLink:
         return element.isLink();
     case CSSSelector::PseudoVisited:
         return element.isLink() && context.visitedMatchType == VisitedMatchEnabled;
     case CSSSelector::PseudoDrag:
         if (m_mode == ResolvingStyle) {
-            if (context.inRightmostCompound)
+            if (context.inRightmostCompound) {
                 context.elementStyle->setAffectedByDrag();
-            else
+            } else {
+                context.elementStyle->setUnique();
                 element.setChildrenOrSiblingsAffectedByDrag();
+            }
         }
         return element.layoutObject() && element.layoutObject()->isDragging();
     case CSSSelector::PseudoFocus:
         if (m_mode == ResolvingStyle) {
-            if (context.inRightmostCompound)
+            if (context.inRightmostCompound) {
                 context.elementStyle->setAffectedByFocus();
-            else
+            } else {
+                context.elementStyle->setUnique();
                 element.setChildrenOrSiblingsAffectedByFocus();
+            }
         }
         return matchesFocusPseudoClass(element);
     case CSSSelector::PseudoHover:
         if (m_mode == ResolvingStyle) {
-            if (context.inRightmostCompound)
+            if (context.inRightmostCompound) {
                 context.elementStyle->setAffectedByHover();
-            else
+            } else {
+                context.elementStyle->setUnique();
                 element.setChildrenOrSiblingsAffectedByHover();
+            }
         }
         if (!shouldMatchHoverOrActive(context))
             return false;
         if (InspectorInstrumentation::forcePseudoState(&element, CSSSelector::PseudoHover))
             return true;
         return element.hovered();
     case CSSSelector::PseudoActive:
         if (m_mode == ResolvingStyle) {
-            if (context.inRightmostCompound)
+            if (context.inRightmostCompound) {
                 context.elementStyle->setAffectedByActive();
-            else
+            } else {
+                context.elementStyle->setUnique();
                 element.setChildrenOrSiblingsAffectedByActive();
+            }
         }
         if (!shouldMatchHoverOrActive(context))
             return false;
         if (InspectorInstrumentation::forcePseudoState(&element, CSSSelector::PseudoActive))
             return true;
         return element.active();
     case CSSSelector::PseudoEnabled:
         if (element.isFormControlElement() || isHTMLOptionElement(element) || isHTMLOptGroupElement(element))
             return !element.isDisabledFormControl();
         if (isHTMLAnchorElement(element) || isHTMLAreaElement(element))
@@ skipping 311 matching lines @@
 }
 
 bool SelectorChecker::matchesFocusPseudoClass(const Element& element)
 {
     if (InspectorInstrumentation::forcePseudoState(const_cast<Element*>(&element), CSSSelector::PseudoFocus))
         return true;
     return element.focused() && isFrameFocused(element);
 }
 
 }