I've found that method unreliable - better just to put an apostrophe in
front of the = to turn it into text. Then it can be copied into another
cell. To build up some complex and longer formulae I often join smaller
(text) ones together with a formula like =A1&A2&A3, then fix the values
of this formula, and maybe add some more to it in another cell.

Hope this helps.

Pete