Underscore: Erro de validação, array é _.isObject () verdadeiro?

var object = {a: 1, b: 2};
console.log('object: has object', _.isObject(object)); //true
console.log('object: has array', _.isArray(object)); //false
console.log('object: has', toString.call(object)); //[object Object]

var object2 = {t: [{a: 1, b: 2}, {c: 3, d: 4}]};
console.log('object2: has object', _.isObject(object)); //true
console.log('object2: has array', _.isArray(object)); //false
console.log('object2: has', toString.call(object2)); //[object Object]

var array = [1, 2];
console.log('array: has object', _.isObject(array)); //true
console.log('array: has array', _.isArray(array)); //true
console.log('array: has', toString.call(array)); //[object Array]

var array2 = [{a: 1, b: 2}, {c: 3, d: 4}];
console.log('array2: has object', _.isObject(array2)); //true
console.log('array2: has array', _.isArray(array2)); //true
console.log('array2: has', toString.call(array2)); //[object Array]