Constrained By creates an error

I have three entities, ContactRoles, Relations and Locations. 1 Relations object is associated with multiple Locations objects. 1 Relations object is associated with multiple ContactRoles objects. Multiple Locations objects are associated with multiple ContactRoles objects. On a page to define ContactsRoles, the user can select a Relation first via a reference selector, and after that he should be able to select one or more locations via a reference set selector. The Locations must be constrained by the chosen Relation. However, as soon as I chose 'Constrained by: ContactRolesRelations/Relations/LocationsRelations/Locations', the modeler pops up an error: 'An error occurred while checking the project for errors'. Details are 'System.NullReferenceException...' The Error list stays empty, as the Modeler can't check errors due to an error (funny). If I reopen the Constrained By window, TWO pathes are selected instead of one, nevertheless the Properties windows says I have selected just 1 path. It seems it doesn't matter changing associations; I tried 1-1, 1-* and - for all associations. Does this problem sounds familiar? What am I doing wrong?
1 answers

Found it, it is probably a bug in 5.0.0-beta6. After installing Modeler 5.0.0.beta7 everything works intuitive as before.