According to discussion at https://groups.google.com/forum/#!topic/mongodb-dev/tJMdvcpGq6Y, it seems as if the server dispatches OP_COMMAND requests based on the wire protocol "command name" field, but the network layer never verifies that the "command name" field matches the first element of the command request. This can yield confusing error messages in command execution (as exhibited by the thread above), and can possibly trip an assertion if any command implementations assert that the first field of the command request object is the expected command name.