I noticed this with the node-mongodb-native driver at v2.2, when we started using schema validations.

Any violation of a schema validator will cause MongoDB to not accept the insert/update, but the driver will return result:

anyway. If the op is an insert, it'll also return the "inserted" doc, and add an .insertedId ObjectId property, which of course matches nothing in the database since the insert op failed.

I thought it might be because 2.2 of the driver predated the schema validation feature, but having just upgraded to v3.0, I can confirm that the issue remains.

It seems to me like a bug, but maybe I need to be schooled a bit?

Cheers,
Daniel