If you de-select a field from the Data area, it is removed totally, and
you have to drag it back in again.

Is there no way around this? I tried dragging to the row field as you
recommend, but its numerical data so having it in the row area is
useless. This is the most ridiculous thing... why would this filter
operate differently than every other filter drop-down. I need for my
users (who know very little about excel and nothing about pivot
tables) to be able to select which of 3 data items will be displayed
without having to display the pivot table toolbar, display the pivot
table fields, and drag the fields back and forth.