mat-expansion-panel re-renders multiple times in a very simple case (no animation, OnPush).

[mfursov]

What is the expected behavior?

mat-expansion-panel updates (renders) exactly once when there is no reason to do it multiple times.

What is the current behavior?

mat-expansion-panel renders at least 2 times ([@.disabled]="true"+ ChangeDetectionStrategy.OnPush)
or even more times if animation is enabled (default) and change detection mode is Default.

What are the steps to reproduce?

https://stackblitz.com/edit/angular-rj4nhe?file=app%2Fexpansion-overview-example.ts

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

7.2.1, Chrome 71

Is there anything else we should know?

It is very important not to have "unexpected" behavior (multiple rendering) because it affects performance metrics. If multiple rendering is "expected" I would suggest to mention about it in docs.

[josephperrott]

It looks like the expansion panel does not rerender entirely multiple times, though change detection seems to be run multiple times unnecessarily.

[snibbo]

Is there any workaround? My panel is jumping up and down :(