The Constituent Attributes Merge Task is designed to work as follows:
One-per Record Attributes
If the target does not have a one-per-record attribute and the source constituent does have one of that type, the program copies the source’s one-per-record attribute to the target.
Duplicate One-per-Record Attributes
The program does not allow constituents to have one-per-record attributes of the same type. If the source and target have attributes of the same type that only support one attribute per record, the merge task excludes the source’s attribute. If the merge task excludes a source’s attribute, it deletes it from the source.
CRM users may notice that constituent attributes remain on the source constituent’s record after merging duplicate constituent records.