When I export a relationship field which has the id "artist_art" (note the underscore) to JSON, the JSON properly includes
"id": "artist_art". However, when I import that same JSON using MB Relationships, the relationship field is created with the ID "artist-art" (note the hyphen). MB import is turning the underscore into a hyphen, or perhaps it is ignoring the
id field entirely and recreating the
id from other elements of the JSON.
This can cause significant problems when there is pre-existing data in the database which has the original ID. MB Relationships should always use the
id found in the JSON when importing relationships.
This may be true of other MB importers as well, we have not yet tested the others. This would be less evident in other imports, though, since those IDs are not used to retrieve data as in the relationships. Still, on principle, if an ID is specified, then that ID should be used unless it is in conflict with another ID.