title: When will a Comparer make Sort throw an ArgumentException?
body: <p>The documentation for <a href="http://msdn.microsoft.com/en-us/library/k3e17y47(VS.80).aspx" rel="nofollow noreferrer">Sort</a> says that Sort will throw an ArgumentException if "The implementation of comparer caused an error during the sort. For example, comparer might not return 0 when comparing an item with itself."</p>
  
  <p>Apart from the example given, can anyone tell me when this would otherwise happen?</p>