My question is stupid but simple:

I have two spreadsheets, spreadsheet A & B, I tried to copy the most
simplest formula from A to B, and i expect the formula is retained in
B, e.g., in cell A1of A : =(1)+(2), then copy to B, it's still
=(1)+(2), very simple right?

The problem is it suddenly not working in one of my office computers,
yes, only one, then weird thing is, when I try the copy function
above, the cell in B only have the value inside, i.e., 3, but not the
formula =(1)+(2), (seems like paste by values, but what I did is only
Ctrl+c and Ctrl+v), when i try to use paste by values, I was promoted
that I need to insert a object something. very strange.

Just would like to know if this related to settings something?

Thanks in advance.