The exact cause would be a question for (old, probably retired) members of the Excel team at MS, but bugs like this were fairly common when working with Windows

The exact cause would be a question for (old, probably retired) members of the Excel team at MS, but bugs like this were fairly common when working with Windows apps that mixed interprocess communication with UI updates. Raymond Chen has a great example of a similar bug here: http://blogs.msdn.com/b/oldnewthing/archive/2005/02/17/375307.aspx http://blogs.msdn.com/b/oldnewthing/archive/2005/02/17/37530...