CSV Save Warning When you Have Multiple Sheets
If you download a CSV file and add new sheets, I have accidentally saved the file in the current CSV file, thereby losing all sheets beyond "Sheet 1".
A simple warning box, applying when you are saving a CSV file with multiple sheets would suffice. It could also suggest saving in XLS.
Ty Lamb commented
Or they should save the other sheets as the original file name "dash" sheet name. But under not circumstances should you be able to save a csv file with multiple pages and just lose your work.