Aurelia event bubbling issue (?), behavior different since 1.0 - aurelia

Question

Reproducible via au new (Aurelia CLI), code below.
It worked perfectly before the update to 1.0.
The problem: When hitting the "Close" button, closePopup() is called but immediately afterwards openPopup() as well. The result is, that the popup does not close. Even click.trigger which shouldn't bubble up the event does not solve the problem.
How to solve this? Why has that behavior changed?
app.html
<template>
<div click.delegate="openPopup()" style="border: 1px solid black; width: 100px; height: 100px">
<div show.bind="_expanded">
Foo <button click.trigger="closePopup()">Close</button>
</div>
</div>
</template>
app.ts
export class App {
_expanded;
openPopup() {
this._expanded = true;
console.log("Opened");
}
closePopup() {
this._expanded = false;
console.log("Closed");
}
}

Answer 1

Solution (event.stopPropagation()):
app.html
<template>
<div click.delegate="openPopup()" style="border: 1px solid black; width: 100px; height: 100px">
<div show.bind="_expanded">
Foo <button click.trigger="closePopup($event)">Close</button>
</div>
</div>
</template>
app.ts
// ...
closePopup(event) {
event.stopPropagation();
this._expanded = false;
console.log("Closed");
}
// ...