When using Suggest surnames when adding family some fields get a value or are cleared.
Clearing a field or filling a field with the default happens when you change the value for Relationship or Gender.
When a user made a a change to a field, it should not be changed again to the default when changing Relationship or Gender (default should be a default when no value was set by the user, not overwrite a user value for a field).
see also Defaults for filling fields on a newly created profile