I´m struggeling a bit with a concept I recently discovered in our own SharePoint 2013.

We have a website with unique permissions and a document library in this site with broken inheritance and therefor also unique permissions.

If I set an user to "read" on the website and to "edit" on the library, all is fine.
But when I delete the user from the website, he also is deleted from the permissions of the library.

Is this correct? I always had the impression, that broken inheritance indeed capsulates the permission rights and all changes done after breaking the inheritance are not touched by actions "around" this object?