Version 2.0.6 of Olingo made the validation of $filter stricter. It actually adds a check for the multiplicity of the navigation properties used in $filter expressions. Using navigation properties with cardinality "TO MANY" in $filter expressions is no longer possible. And indeed this is not allowed by OData v2 protocol. There are some OData services, however, that deviate from the standard in this respect. It should be possible to switch off the strict filter validation in order to integrate with such services. The UriParser should allow passing strictFilter as an argument for the parse method.