Keith,
In the "Settings" tab of the ADP node, select "Field Settings" in the left panel under Settings.
You will see in the middle of the right panel: "How to handle fields that are excluded from modeling:"
The default setting is to "Filter out unused fields" so you merely need to select the other radio button:
"Set the direction of unused fields to 'None'"
Steve
P.S. a workaround would be to perform a (keyless) merge by record order but that shouldn't be necessary.