When you are having to override library permissions where you have previously overridden folder permissions and/or item permissions to break inheritance, BE WARNED that permissions behavior in SharePoint may not be what you’d expect. I’ll explain by demo…
Start by navigating to the target library.
Now go ahead and override item permissions.
Upon completion, you should have new permissions for the item.
Now navigate back to the top site.
Go ahead and override library permissions.
In my case, I removed Members and Visitors from the library level permissions.
Now navigate back to the item again.
You’ll notice some permissions missing.
The conclusion is that breaking inheritance at the library level will override the item level permissions and cause unexpected results.
This can be particularly bad if you’re unaware of this behavior and you have an external facing site that has had item level permissions configured for certain external partners and someone breaks the inheritance on the library level as it could grant access to content to unintended users.
Trackback from your site.