See attached Test.

A detailed description of why this is a problem:

In our service layer, we have methods that expose IQueryable<IEntity> values. The intent is that other services can uses these to perform more detailed queries. Internal to the service, we query against a collection using the concrete type (GetCollection<Entity>()) and return it as an IQueryable<IEntity>(). Enumerations against this object succeed. However, if we do an additional query against it, we get a serialization exception.