The Organization Field is an option to mpa because the field name is actually "Last Name/Organization Name'. It is the field name from the Constituent Marketing query view (which is the query view we use as the Record Source). The same field is also used in the constituent table for both "Last Name" and "Organization Name".

In order to allow this to work, the record source mapping will need to be changed, or changes to how they pull the field names when mapping fields.