I had a comment at the very bottom of http://docs.mongodb.org/manual/reference/replica-configuration/ in mind. `rs.reconfig()` is mongodb shell for `replSetReconfig`:

> The rs.reconfig() shell method can force the current primary to step down and triggers an election in some situations. When the primary steps down, all clients will disconnect. This is by design. Since this typically takes 10-20 seconds, attempt to make such changes during scheduled maintenance periods.