Expansion icon animation is bugged

[julianobrasil]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

When grouped in an accordion (multi=false) and you click in an expansion, the actual opened one should close and its toggle icon should point downwards.

What is the current behavior?

If you start expanding/collapsing the expansions by clicking in the header of other panels, the toggle icon is not being updated. And when it is, the animation is not smooth.

What are the steps to reproduce?

1 - Open one panel
2 - Click in the header of the other panel and see the toggle icon freezed in the upward direction

Plunk: https://plnkr.co/edit/lmR0Fp?p=preview

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

Latest build (see the plunk)

[julianobrasil]

@mackelito

[crisbeto]

Should be fixed by #5650. Closing as a duplicate of #5623.

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