{} Brackets

Can Someone please help me
I have a formula

{=IF(OR(D9=M4:S99),"m")}

For instance

This formula works
But when i click in the cell to edit the formula the {} (at the beginning and end) disapear and the formula no longer works.
If i add them back manually the formula still does not work.

How can i edit these formulas without stopping them working.

Many Thanks

Sorry if this is a noob question