1. Initialize replica set like this: { "_id" : "test", "version" : 1, "members" : [ { "_id" : 0, "host" : "myServer:27001", "priority" : 50 }, { "_id" : 1, "host" : "myServer:27002", "priority" : 50 }, { "_id" : 2, "host" : "myServer:27003", "priority" : 0 }, { "_id" : 3, "host" : "myServer:27004", "priority" : 10 }, ] } 2. Add a row, using w:2 (works) db.test.insert({x:1}, { writeConcern : { w:2, wtimeout: 15000 }}) 3. Reconfigure replica set with this configuration: { "_id" : "test", "version" : 2, "members" : [ { "_id" : 0, "host" : "myServer:27001", "priority" : 50 }, { "_id" : 1, "host" : "myServer:27002", "priority" : 50 }, { "_id" : 2, "host" : "myServer:27003", "priority" : 0 } ] } 4. Assuming the same server is primary before and after the reconfig, this will work: db.test.insert({x:2}, { writeConcern : { w:2, wtimeout: 15000 }}) 5. Failover to the server on 27002 (rs.stepDown()) 6. This operation times out: db.test.insert({x:3}, { writeConcern : { w:2, wtimeout: 15000 }}) 7. Fail back to 27001 8. This works again: db.test.insert({x:2}, { writeConcern : { w:2, wtimeout: 15000 }})