When sending a write concern of { j : true } to a server with journaling disabled server versions 2.2.x. and 2.4.x respond as follows:

"{ \"n\" : 0, \"connectionId\" : 4, \"jnote\" : \"journaling not enabled on this server\", \"err\" : null, \"ok\" : 1.0 }"

We were not properly detecting this as an error because we assumed that { ok : 1 } meant everything was OK.