Hi agree with tresco.
Paul your field Currency_P have some strange values.
when I try to get below expression
It not returning the same values.
Other then that the solution proposed by jagan must work.
may be jagan can help you here.
Did you add Select In Field Trigger for the Field? Check this thread hope it helps you. Can you attach some sample file
Select in Field Trigger with Single or Multiple values
In the above is TMY and TID are fields are values, if those are values then then try this
Hope this helps you.