Aurelia验证不适用于派生类

Question

我在typescript 1.6和最新的aurelia中有以下场景：

import {ensure, Validation} from "aurelia-validation";
import {ValidationGroup} from "aurelia-validation";

@inject(Validation)
export class BaseClass {

  validation: ValidationGroup;

  @ensure(function (it) { it.isNotEmpty().hasLengthBetween(3, 10) })
  firstName: string;

  constructor(validation: Validation) {
    this.validation = validation.on(this, null);
  }
}

@inject(Validation)
export class DerivedClass extends BaseClass {

  @ensure(function (it) { it.isNotEmpty().hasLengthBetween(3, 10) })
  lastName: string;

  constructor(validation: Validation) {
    super(validation);
  }

  submit() {
    this.validation.validate().then((value) => { /* */ });
  }
}

问题在于，当我在derived-class.html视图中提交表单数据时，只有lastName属性得到验证，而firstName属性甚至没有在验证中列出基。