When you perform an upsert with a custom _id the upserted field is not returned by GLE meaning the bulk api does not register it correctly as a upsert.
Beneath is the node.js test that replicates this behavior
When you perform an upsert with a custom _id the upserted field is not returned by GLE meaning the bulk api does not register it correctly as a upsert.
Beneath is the node.js test that replicates this behavior