When creating a new MongoClient instance with valid host/port parameters, but no MongoDB running there, I would expect a MongoException to be thrown. This is not the case. I can even use the MongoClient instance to get a DB instance via getDB() and subsequently a collection instance via getCollection(), again without being actually connected and any exception. I also tried getConnector().isOpen() to verify whether the connection was established and it returned true, without a running server. The latter issue might be me misinterpreting the API though.

Others (see user "litiales") are observing this as well.