Which @angular/* package(s) are the source of the bug?

Don't known / other

Is this a regression?

No

Description

This code is supposed to hide the .box when Toggle is clicked. It will not hide. It will animate out as expected, but then reappear.

The following things must be true for the issue to exist, otherwise there is no problem:

• animate.leave must be present.
• The component must be nested.
• provideAnimationsAsync must be configured.
• The parent or a container's sibling @Component must have animations, even if empty.

I'm using signals in the example, but it works with ordinary properties too.

import { Component, signal } from '@angular/core';

@Component({
  selector: 'app-container',
  template: `
    <button (click)="visible.set(!visible())">Toggle</button>
    @if (visible()) {
      I will hide
      <div class="box" animate.leave="leave">And I won\'t</div>
    }
  `,
  styles: [`
    .box {
      background: red;
    }

    @keyframes fade-out {
      from { opacity: 1; }
      to   { opacity: 0;  }
    }

    .leave { animation: fade-out 1000ms; } 
  `],
})
export class Container { // <-- Must be nested
  readonly visible = signal(true);
}

@Component({
  selector: 'app-root',
  template: `<app-container />`,
  imports: [
    Container,
  ],
  animations: [], // <-- Necessary to break things
})
export class App {
}

Please provide a link to a minimal reproduction of the bug

https://studio.firebase.google.com/animate-leave-27515706

Please provide the exception or error you saw

Please provide the environment you discovered this bug in (run ng version)

@angular-devkit/architect    0.2003.6
@angular-devkit/core         20.3.6
@angular-devkit/schematics   20.3.6
@schematics/angular          20.3.6
rxjs                         7.8.2
typescript                   5.9.3
zone.js                      0.15.1

Anything else?

Why is this important?

I was using PrimeNg and had <p-confirmDialog /> in one of the root components. It had some animations defined and it was breaking animate.leave in one of my components.
The library and this pattern is quite common and when you encounter the issue it's hard to understand what the problem is.