Can a calculation go wrong in MS Excel?

There is such a thing called a rogue!

It did once in all these years (30 yrs) I have used EXCEL. I simply cannot figure it out. I include a screenshot of what I observed.

As a workaround, I deleted the line and recreated it. Everything OK.

How do you save an Excel file as a text file?

It is very easy. Use the menu item "Save As" as shown in this example.