Cells A!, B1, C1 and D1 have a "General" format:

A1 contains 5
B1 contains 6
C1 contains 2
D1 contains formula =A1+B1 so 11 is displayed.

When I change the formula in D1 to =A1+C1 and press "Enter", the
format of D1 changes to "Text" so "=A1+C1" is displayed.

I then have to change the format of D1 to "General" and press F2.
Now 7 is displayed in D1.

(This also happens if the four cells have a "Number" format).

How can I keep the cell's original format?

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