A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
This is a widely reported problem with the copy and paste functionality in Excel, Microsoft have indicated they are working to resolve the problem and they will release a patch for the problem as soon as they have found the underlying cause of the problem.
In the meantime, many people indicate if you copy a cell, then rather than pasting, use Paste Special, and on the resulting dialog box, select to past either data or formula and that should work until Microsoft have resolved the problem.