The document library toolbar does not respect the folder permissions.
After spending some time on the problem, i realized that the toolbar in the document library (containing Actions buttons) actually is only loaded ONCE upon instantiation of the portlet. Other buttons such as "AddButton" is actually reloaded in the document library main.js so this is not an issue when browsing through different folders.
Every further browsing through the folders does not refresh the privileges.
The toolbar is displayed by default if the user is logged in. However the options available shall be dependent on the logged-in user permissions as well.