Although unversioned 2dsphere indexes are executed as V1, $listCatalog / $indexStats / listIndexes currently don't return "2dsphereIndexVersion" field for them. This affects tools (mongosync, mongodump/mongorestore, mongomirror) that read index specifications from a source cluster and create them on a target cluster. Inconsistencies in index definitions can occur through migration if a 2dsphere index without index version field exists on the source cluster and is executed as a V1 index but is created as a V3 index on the target (due to the default behavior of index creation).