A cell has a "General" format, the cell contains a formula and the
result of the formula is displayed in the cell.

When I change an expression in the formula, the cell's format changes
to "Text" and the formula is displayed in the cell.

I then have to change the cell's format back to "General" then press
F2 to get the formula's result to be diplayed in the cell.

How can I prevent the cell's format from changing from "General" to
"Text"?