MatTable inside MatTable with expandable columns

[alexmitu]

Hello.
I have today upgraded the application to Angular 9 and I've noticed some strange behavior. Whenever I'm adding a table inside a mat expandable column, I'm getting an error "ERROR
Error: Duplicate column definition name provided: "name1"."

I have attached two stackblitz links to show the error:
On Angular 8.2:
https://stackblitz.com/edit/angular-wpefut
On Angular 9:
https://stackblitz.com/edit/angular-adqf7a

Same code, different angular versions.

[codymikol]

Please submit Angular Material questions here and issues here. This repo is for AngularJS Material.

[Splaktar]

Duplicate of angular/components#18768.