Excel 2007 Losing Formatting

I have a user that is using Excel 2007 SP2 with all current updates. There is an Excel files (xlsx format) that he appends data to that seems to lose all formatting about once a week. He opens the file and Excel states that it has to repair and then removes all formatting.

The user appends csv files by opening them in another instance of Excel, copying the cells out and pasting them into the main Excel spreadsheet. This only happens when opening this particular Excel spreadsheet. I've also noticed if the Styles on the Home tab (Home Tab - Styles section, pictured below) are all the same when the user saves the file and exits it out, the next time he opens the file it will probably be corrupt and need to be repaired. I've looked all around and have not found a solution for this. Can anyone help??????