Recently, whenever I open the Excel and close it, it always prompts me to save changes to book1 even though I have not made any changes. This started happening very recently. It is very strange that once the Excel is open and if I create new workbook and close it, it does not prompt me. I have verified that there is no hidden spreadsheet.
I found out that it is due to MySQL for Excel component installed when I installed MySQL. I removed this component and problem went away.