New Post: Adding formula results save prompt when excel file is closed

I just added the following line in my .net application:

ws.Cell(3, 5).FormulaR1C1 = "RC[-1] - RC[-2]";

Formula works as expected when I open resulting excel file. But when I click close button excel asks me to save changes. How to avoid this prompt? I upgraded to DocumentFormat.OpenXml 2.5 and ClosedXML 0.75; the issue still remains.