Enable client generated keys for associations
In V1 of WCF RIA Services, EntityCollection and EntityRef do not filter entities if they are in an EntityState of New. This is by design to allow for entities that have server generated primary keys. If the primary key is client-generated (i.e. a GUID) this limitation is not needed.
Here is an example of problems caused by the current behavior: http://forums.silverlight.net/t/235573.aspx/1?Only+setting+an+Id+causes+only+half+of+the+reciprocal+relationships+to+connect+up