Don’t use spreadsheets on a Mac.
In Numbers, I found that if I select some cells containing numbers with some others that are empty, in order to specify their format, Numbers inserts random values in the empty cells. Very useful for accounting, that. I also caught it emptying the contents of selected cells, when selecting. Very useful for accounting, that.
Actually, don’t bother with Mac Excel either. If you put a formula in a cell, select and copy that formula, paste it in another cell elsewhere, and edit the formula you’ve just pasted, Excel carefully deletes the copy you’re working on and corrupts the version from which you copied.
I guess this is some kind of bizarre U/I guideline that’s gone wrong. Perhaps this is why Apple haven’t got the business market. I’ll stick with Windows. The U/I for spreadsheets there isn’t entirely stupid.