Dialog/Overlay doesn't block scrolling if page dimensions change

[diminutivesloop]

Reproduction

Use StackBlitz to reproduce your issue: https://stackblitz.com/edit/components-issue-kktbjg

Steps to reproduce:

1. Click the Open Dialog button.
2. Wait 3 seconds for images to appear behind the dialog.

Expected Behavior

When a dialog is open and scroll blocking is enabled the content behind the dialog should not be scrollable.

Actual Behavior

If the content behind the dialog is not scrollable when the dialog is opened and then becomes scrollable while the dialog is still open then scroll blocking does not work. This can happen either when new page content loads or when the window is resized to be smaller.

Environment

• Angular: 8.0.0
• CDK/Material: 8.0.0
• Browser(s): Chrome 74.0.3729.169
• Operating System (e.g. Windows, macOS, Ubuntu): Windows

[csbenjamin]

It takes a lot of time for me to figure out that this was the problem... I thought that I was not using the scroll blocking correctly. I was going to open a new issue but found this one.

[jeremie-lucca]

Same issue here. I wonder why cdk-global-scrollblock is added only if there is no scroll on the page, considering it's common from users to manually resize the page.