Strange SQL error (nodereferrer.nid = ...)

Hallo,
Nodereferrer seems is exactly what I need for our school website.

My use case

• I have a Content Type class. It has a noderefernce field field_class_my_exercises(multiple values) of the content type exercise
• The content type exercise has a nodereferrer field field_exercises_used_in_classes
• On the node page of an exercise (the one that list all values of a node) all refernced classes are listed (=> it works)

The Problem

Now I try to create a view that lists all exercises of a class.

• I create a view view_class_list_exercises
• Tableview, field is Node:Title

Ok, now in I only want to create a view that catches the Nodes of type exercise that refer to class with node:id 131, I added the filters node:type=exercise and nodereferrer:field_exercises_used_in_class.

But I get this error

user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''131') LIMIT 0, 10' at line 1 query: SELECT node.nid, node.title AS node_title, node.changed AS node_changed FROM node node WHERE (nodereferrer.nid in '131') LIMIT 0, 10 in ...

This query cannot work because of WHERE (nodereferrer.nid in '131'), the syntax is wrong and nodereferrer is no table??

Any guess?
thx in advance