Unable to scroll behind overlays (mat-menu, mat-select, etc)

[adamdport]

Bug, feature request, or proposal:

When a mat-menu, mat-select, or any other overlay that uses a repositionScrollStrategy is open, the user cannot scroll

What is the expected behavior?

According to the docs,

RepositionScrollStrategy will re-position the overlay element on scroll.

What is the current behavior?

When an overlay is open, scrolling is blocked

What are the steps to reproduce?

I'm having trouble recreating it in a stackblitz, but it's broken in the material docs themselves: https://material.angular.io/components/menu/overview

Open a menu and then try to scroll the page

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

According to the docs,

RepositionScrollStrategy will re-position the overlay element on scroll.

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

"@angular/core": "6.0.7",
"@angular/material": "6.3.2",

Is there anything else we should know?

[crisbeto]

This is a side-effect of the backdrop which will be fixed by #7779. You can also work around it by making the body the scrollable element. Closing as a duplicate of #6927.

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}