Missing rows from views if referenced node is not set

Hello,

I have 3 content types: Teachers, Courses and Course materials. There is a node references field in Course connecting it to a teacher and one in Course materials connecting it to a given course. I grant rights to users with Node access user reference and Node access node reference modules so they can view and edit only the nodes they are referenced to (either directly or indirectly).
I'd like to show the courses of a teacher and the number of the attached course materials for each course. I created a view as an EVA display with a contextual filter which use the nid of node the view is attached to. I also created a relationship with the reverse field in Course material refering to the course. (and let the Require this relationship checkbox unchecked.)
The course and the number of attached materials is properly displayed but courses without materials are missing from the list. I checked the permissions of authenticated users and all involved nodes (courses, materials) can be viewed (and updated) by their 'owner'. So I don't really understand why the view doesn't show them.
I found a workaround: If I disable SQL rewriting in Views UI all necessary courses are displayed. But I think it's quite weird because the permissions of the individual nodes are OK. How can I figure out which access restrictions are disabled by this options? And I'd greatly appreciated if anyone can suggest me a proper solution.