Unusual formula
 

Hi

I am using ex2007 and I have been extending a large sheet that has already many formulas including countif and simple totals

However when I double click a cell to look at the calculation steps or copy a part (ie the bracketed part of a countif formula) when I then leave the cell it then reads as 0

I have checked that I have not inadvertantly changed the cell format, and am v. confused any help would be gladly received!