The inline documentation for the magnifier feature is slightly confusing in a way that could frustrate users: since it's not mentioned that holding down ⇧ only toggles the magnifier while resizing the selection rectangle, there's the very likely potential for the user to hit ⇧ during another time, notice that nothing has happened, and conclude that the feature is broken.
This patch improves the documentation to make it clear under what circumstances holding down the ⇧ key will do something.