I've run into a difference in behavior between Excel 2010 and Excel 2003. It involves worksheets containing references to worksheet-level defined names in array formulas, and occurs when such worksheets are either copied or renamed. Whereas in Excel 2003, all the 'sheet name'! strings are automatically adjusted to the new (or renamed) sheet name, in Excel 2010, they retain the old sheet name! Neither A1-style references nor references in non-array formulas exhibit the problem. So far I can verify this behavior in both Office Professional and Office Professional Plus SP1. Am I missing something, or is this a bug?