Book1 requires me to choose save each time i close excel
 

Recently Excel has started to require me to save Book1 when i close Excel,
even when i have opened another file. Previously if i opened another file,
only that file would be open and Book1 would disappear. Now when i open
another file, Book1 stays open as well as the other file, and when i close
excel, i am forced to choose save or not for Book1 before closing, even if it
is untouched. Not the end of the world but bloody annoying