DBClientCursor returns a getMore() error as a result (in some cases)

In at least some cases, the DBClientCursor treats an error on getMore() as a query result, returns it to the client as a document, and stops iterating the cursor. There isn't any indication to the client, at least to a mongo shell client, that the invalid getMore document is not just a document in the collection.

see DBClientCursor::dataReceived - the error is flagged, but this does not affect what is returned.

Unclear if this affects master.