Angular2 + RxJS BehaviorSubject订阅不适用于所有组件

我正在尝试在组件之间进行某种形式的通信，因此我在这样的组件中使用带有BehaviorSubject和Subscription的服务:

I'm trying to make some sort of communication between my components, so I'm using a service with a BehaviorSubject and Subscription in the components like this:

服务(与问题相关的代码):

Service (code related to the problem):

import { BehaviorSubject } from 'rxjs/BehaviorSubject'

private _clientModalActionSource = new BehaviorSubject<string>('')
modalAction$ = this._clientModalActionSource.asObservable()
public updateClientModalAction(action) {
   this._clientModalActionSource.next(action)
   console.log('sent')
}

组件A:

this._api.updateClientModalAction(id)

组件B:

import { Subscription } from 'rxjs/subscription'

private _subscription: Subscription
ngOnInit() { this._subscription = this._api.modalAction$.subscribe(res => {
   this.refreshModal(res)
   console.log('received')
})}

如果组件B是组件A的子组件，则此方法运行良好，但是如果组件A是根组件，而组件B在其组件<router-outlet>(或相反)之内，则订阅什么都没有收到，我只能得到sent在控制台中.

This is working perfectly if Component B is child of Component A, but if A is the root component and B is inside its <router-outlet> (or the opposite) nothing is being received to the subscription, I only get sent in the console.

我在做什么错了?