There are two ways they could have done this.

A) The DF remembers what you queued for last, and gives you a button to clear all selections.

B) The DF clears all selections whenever you finish a duty, and gives you a button to restore previous selections.

Since farming is a thing that happens often, (A) is the correct choice for this game. If you often forget that you're queued for things, even though it clearly shows you a list of the things you're queued for, train yourself to press the clear all button whenever you open the DF so you don't queue for the wrong things.