An object may become a column spanner or cease to be one even if column-span doesn't change.

Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 236 matching lines @@
     }
 
     if (isDocumentElement() || isBody()) {
         document().view()->recalculateScrollbarOverlayStyle();
         document().view()->recalculateCustomScrollbarStyle();
     }
     updateShapeOutsideInfoAfterStyleChange(*style(), oldStyle);
     updateGridPositionAfterStyleChange(oldStyle);
 
     if (LayoutMultiColumnSpannerPlaceholder* placeholder = this->spannerPlaceholder())
-        placeholder->updateMarginProperties();
+        placeholder->layoutObjectInFlowThreadStyleDidChange(oldStyle);
 }
 
 void LayoutBox::updateShapeOutsideInfoAfterStyleChange(const ComputedStyle& style, const ComputedStyle* oldStyle)
 {
     const ShapeValue* shapeOutside = style.shapeOutside();
     const ShapeValue* oldShapeOutside = oldStyle ? oldStyle->shapeOutside() : ComputedStyle::initialShapeOutside();
 
     Length shapeMargin = style.shapeMargin();
     Length oldShapeMargin = oldStyle ? oldStyle->shapeMargin() : ComputedStyle::initialShapeMargin();
 
@@ skipping 4525 matching lines @@
 bool LayoutBox::canRenderBorderImage() const
 {
     if (!style()->hasBorderDecoration())
         return false;
 
     StyleImage* borderImage = style()->borderImage().image();
     return borderImage && borderImage->canRender(*this, style()->effectiveZoom()) && borderImage->isLoaded();
 }
 
 } // namespace blink