You can disable this feature by:
Tools|Options|Edit tab|Uncheck Allow cell drag and drop

But this will disable dragging and dropping (and the autofill button in the
lower right corner of the selected cell).

KIM W wrote:

Can one disable the ittirating Excel behavior of moving you to another cell
when you double click on the border of a cell?
We do a lot of in cell editing, and if one accidentally double clicks on top
border of cell, it moves you to the next empty or last occupied cell above
you. (Just like ctl+Up Arrow, etc.) This can move you to an unwanted location
far away from where you were editing.

--

Dave Peterson