Why is the Entity Framework inserting when it should update?

Question

I use the following RIA Services call to register and return a Project entity.

// On Server; inside RIA Domain Service
[Invoke]
public Project CreateNewProject(String a_strKioskNumber)
{
  Decimal dProjectID = ObjectContext.RegisterProjectNumber(a_strKioskNumber)
                       .FirstOrDefault() ?? -1m;

  // Tried this but it returned zero (0)
  //int nChanged = ObjectContext.SaveChanges();

  var project = (from qProject in ObjectContext.Projects.Include("ProjectItems")
                 where qProject.ID == dProjectID
                 select qProject)
                 .FirstOrDefault();

  if (project == null)
    return null;

  return project;
}

As you can see, it calls a stored procedure that returns a project ID. It uses this ID to look up the Project entity itself and return it. When the Project entity is returned to the client it is detached. I attach it to the DomainContext and modify it.

// At Client
_activeProject = a_invokeOperation.Value; // <-- Detached
_context.Projects.Attach(_activeProject); // <-- Unmodified

if (_activeProject != null)
{
  _activeProject.AuthenticationType = "strong"; // <-- Modified
  _activeProject.OwnerID = customer.ID;
  _projectItems.Do(pi => _activeProject.ProjectItems.Add(pi));
  _activeProject.Status = "calculationrequired";
} 

At this point it has an entity state of Modified. When I submit changes it gives me an exception regarding a UNIQUE KEY violation as if it is trying to insert it rather than update it.

// At Client
_context.SubmitChanges(OnProjectSaved, a_callback);

I'm using the same DomainContext instance for all operations. Why should this not work?
What's going wrong? This is rather frustrating.

Edits:

I tried this (as suggested by Jeff):

[Invoke]
public void SaveProject(Project a_project)
{
  var project = (from qProject in ObjectContext.Projects
                 where qProject.ID == a_project.ID
                 select qProject)
                 .FirstOrDefault();

  project.SubmitDate = a_project.SubmitDate;
  project.PurchaseDate = a_project.PurchaseDate;
  project.MachineDate = a_project.MachineDate;
  project.Status = a_project.Status;
  project.AuthenticationType = a_project.AuthenticationType;
  project.OwnerID = a_project.OwnerID;
  project.ProjectName = a_project.ProjectName;
  project.OwnerEmail = a_project.OwnerEmail;
  project.PricePerPart = a_project.PricePerPart;
  project.SheetQuantity = a_project.SheetQuantity;
  project.EdgeLength = a_project.EdgeLength;
  project.Price = a_project.Price;
  project.ShipToStoreID = a_project.ShipToStoreID;
  project.MachiningTime = a_project.MachiningTime;

  int nChangedItems = ObjectContext.SaveChanges();
}

It did absolutely nothing. It didn't save the project.

Answer 1

What happens if you add a SaveProject method on the server side and send the object back to the server for saving?

I've not done EF with RIA Services, but I've always sent my objects back to the server for saving. I'm assuming that SubmitChanges call you are making wires up everything properly for you for sending it back to the server, but perhaps it is doing something wrong and handling it manually will fix it.