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

Source/core/style/ComputedStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 158 matching lines @@
 StyleRecalcChange ComputedStyle::stylePropagationDiff(const ComputedStyle* oldStyle, const ComputedStyle* newStyle)
 {
     if ((!oldStyle && newStyle) || (oldStyle && !newStyle))
         return Reattach;
 
     if (!oldStyle && !newStyle)
         return NoChange;
 
     if (oldStyle->display() != newStyle->display()
         || oldStyle->hasPseudoStyle(FIRST_LETTER) != newStyle->hasPseudoStyle(FIRST_LETTER)
-        || oldStyle->columnSpan() != newStyle->columnSpan()
         || !oldStyle->contentDataEquivalent(newStyle)
         || oldStyle->hasTextCombine() != newStyle->hasTextCombine()
         || oldStyle->justifyItems() != newStyle->justifyItems()
         || oldStyle->alignItems() != newStyle->alignItems())
         return Reattach;
 
     if (oldStyle->inheritedNotEqual(*newStyle))
         return Inherit;
 
     if (*oldStyle == *newStyle)
@@ skipping 1549 matching lines @@
 }
 
 void ComputedStyle::copyChildDependentFlagsFrom(const ComputedStyle& other)
 {
     setEmptyState(other.emptyState());
     if (other.hasExplicitlyInheritedProperties())
         setHasExplicitlyInheritedProperties();
 }
 
 } // namespace blink