A button ripple effect appears again after a dialog is closed

#### Bug, feature request, or proposal:

A bug.

#### What is the expected behavior?

The ripple darkening effect shouldn't appear on a button after a dialog is closed.

#### What is the current behavior?

A ripple / CSS effect appears on the 'invoking' button again after the dialog is closed. Should be only one one animation cycle when the button is pressed.

#### What are the steps to reproduce?

From:
https://material.angular.io/components/dialog/overview

On:
Firefox 56.0.2
Chrome 61.0.3163.100

Pressing the "Pick one" button, the ripple effect is played and the dialog is opened, then closing the dialog in any way return the effect on the button.

https://i.imgur.com/oOmbAmS.gif

#### What is the use-case or motivation for changing an existing behavior?

It's visually 'bugged'

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

It appears in both local build
Angular 5
Material 5.0.0-rc0

And with a refreshed documentation / example page

#### Is there anything else we should know?