Add Modern Page with Permission might break SiteAssets permission

First of all - the Issue is not code/pnp specific and can be validated in UI as well. However, we had Templates provisioned which did result in wrong permission settings on the Site Asset Library -that's why i report it here.

Use Case:
-Only site owners should be allowed to create modern pages, Members and Visitors should have read only
-The Site owners should not be allowed to change the welcome page to preserve a common layout

Solution:
-Break Role Inheritance on SitePages-Library and change permission for Owners to contribute and Members/Visitors to read
-Break Role Inheritance on WelcomePage and set Owners,Members,Visitors to read (only sitecollection admin can edit)

Issue:
The change of Permission at the WelcomePage seems to trigger a EventHandler which set's on SitesAssets-Library the same permission as on the SitePages-Library. In my example -contribute for owners and read for all others.

As the One-Note-Folder is in the SiteAssets-Library, the Members would loose write permission in our example.
The user might or might not recognize that his changes in the One-Note-Client-App are not synced, which means we end up in a painful mess.

@jansenbe it's with ms support #‎31795834‎

Start by reproducing the permission change in the UI using the SitePages library, WelcomePage, and SiteAssets library. Verify whether changing WelcomePage permissions also changes SiteAssets permissions, especially Members' write access to the OneNote folder. Done means the requested SitePages and WelcomePage restrictions remain in place without removing required SiteAssets write permission.