If a node is not included in the latest config, when it tries to join the replset, the node will get the new config that doesn't have itself. SERVER-15740 disallow the transition from RS_STARTUP to RS_REMOVED directly due to the implementation of checkQuorumForConfigChange. With Safe Reconfig project, checkQuorumForConfigChange won't talk to the nodes in the new config before installing it, so this won't be a problem.