Cassandra replication factor greater than number of nodes

I am using the datastax java driver for Apache Cassandra (v. 2.1.9) and I am wondering what should happen when I set replication_factor greater than number of nodes. I've read somewhere that Cassandra allows for this operation, but should fail when I will try to save some data (of course it depends on the write consistency level, but I mean the case of ALL).
The problem is that everything works, no exception is being thrown, even if I try to save data. Why?
Maybe the pieces of information which I've read were old, for older versions of Cassandra? One more question, whether it's true, than what would happen when I add another node to the cluster?