why does $.couch.db().bulkSave not work?

gistfile1.js

function inject_script(string){
    var x = document.createElement('script');
    x.src = string
    document.body.appendChild(x);
}

inject_script("http://documentcloud.github.com/underscore/underscore-min.js")
inject_script("https://raw.github.com/boxxxie/underscore_extended/master/underscore_extended_browser.js")

var _users_db = $.couch.db("_users");
_users_db
    .allDocs(
	{
	    include_docs:true,
	    success:function(resp){
		var users = _.chain(resp.rows)
		    .pluck('doc')
		    .reject(function(doc){return /^_design/.test(doc._id)})
		    .value();
		console.log(users)
		var enabled_users = _.map(users,function(user){return _.extend(user,{enabled:true})});
		console.log(enabled_users)
		console.log(JSON.stringify(enabled_users))
		_.each(enabled_users,function(user){_users_db.saveDoc(user)}) //works
		//_users_db.bulkSave(enabled_users) //doesn't work
	    }
	})