Angular2路由器附加组件而不是替换它

包含< router-outlet>的主要组件的标记。看起来像这样

<div *ngIf="authenticated == false">
  <app-login></app-login>
</div>
<div *ngIf="authenticated">
  <div class="page home-page">
    <header class="header">
      <app-navbar></app-navbar>
    </header>
    <div class="page-content d-flex align-items-stretch">
      <div class="sidebar-container">
        <app-sidebar-menu></app-sidebar-menu>
      </div>
      <div class="content-inner">
      <app-page-header></app-page-header>
        <div id="sub-content">
          <router-outlet></router-outlet>
        </div>
        <app-footer></app-footer>
      </div>
    </div>
  </div>
</div>

如果我单击Demo链接，将呈现演示组件，但如果我单击Home链接，则主组件将呈现在DOM中的演示组件上方。点击它们几次将产生这样的DOM

<div _ngcontent-c0="" id="sub-content">
    <router-outlet _ngcontent-c0=""></router-outlet>
  <app-home _nghost-c6="">...</app-home>
  <app-demo _nghost-c7="">...</app-demo>
  <app-home _nghost-c6="">...</app-home> <!-- Why so many here? Should be just either one <app-home> or <app-demo>  -->
  <app-demo _nghost-c7="">...</app-demo>
  <app-home _nghost-c6="">...</app-home>
  <app-demo _nghost-c7="">...</app-demo>
  <app-footer _ngcontent-c0="" _nghost-c5="">...</app-footer>
</div>

路线定义为

export const router: Routes = [
    { path: 'demo',component: DemoComponent,canActivate: [AuthGuard] },{ path: 'home',component: HomeComponent,canActivate: [AuthGuard] }
]

为什么< router-outlet>不替换组件，而是在路由之间切换时添加组件的另一个“实例”？