Every CSV I've ever tried to save from Excel (2010, anyway) says
filename.csv may contain features that are not compatible with CSV (Comma delimited). Do you want to keep the workbook in this format?. Why is this? Is there any way to save CSV files from excel that do not contain this message?
Even the following file (saved as a .csv) will cause this to happen, if you try to save it:
I've even just created a new spreadsheet in excel and tried to save it, and it still shows this message.
I wouldn't care, but I have someone telling me that I'm not formatting CSV files properly because excel shows that warning message, and I'm looking for ammunition to prove it's Excel and not my format (or if it actually is my format, to fix it).