leading underscore in documents fails nano's validation

nano_.js

nano = require('nano')('http://localhost:5984');

nano.db.create('underscore', function(err){
  data = {foo:'bar', _ISNEW:true};
  couchdb = nano.use('underscore');
  couchdb.insert(data, function(err,body) {
    console.log('err:\n'+err+'\nbody:\n'+body);
    console.log('JSON.stringify(err):\n'+JSON.stringify(err,null,2));
  });
});

/* OUTPUT:

err:
Error: Unspecified error
body:
undefined
JSON.stringify(err):
{
  "name": "Error",
  "scope": "couch",
  "status_code": 500,
  "status-code": 500,
  "request": {
    "method": "POST",
    "headers": {
      "content-type": "application/json",
      "accept": "application/json"
    },
    "uri": "http://localhost:5984/underscore",
    "body": "{\"foo\":\"bar\",\"_ISNEW\":true}",
    "jar": false
  },
  "headers": {
    "date": "Mon, 04 Jun 2012 16:55:56 GMT",
    "content-type": "application/json",
    "cache-control": "must-revalidate",
    "status-code": 500,
    "uri": "http://localhost:5984/underscore"
  },
  "errid": "non_200",
  "error": "doc_validation",
  "reason": "Bad special document member: _ISNEW",
  "description": "Unspecified error",
  "stacktrace": [
    "Error: Unspecified error",
    "    at Request._callback (/home/source/project/nodecuizini/node_modules/nano/nano.js:286:39)",
    "    at Request.callback (/home/source/project/nodecuizini/node_modules/nano/node_modules/request/main.js:119:22)",
    "    at Request.<anonymous> (native)",
    "    at Request.emit (events.js:70:17)",
    "    at Request.<anonymous> (/home/source/project/nodecuizini/node_modules/nano/node_modules/request/main.js:521:16)",
    "    at Request.emit (events.js:67:17)",
    "    at IncomingMessage.<anonymous> (/home/source/project/nodecuizini/node_modules/nano/node_modules/request/main.js:483:14)",
    "    at IncomingMessage.emit (events.js:88:20)",
    "    at HTTPParser.onMessageComplete (http.js:137:23)"
  ]
}


*/