Entity Framework 5 :new DBContext does not update current object

[hqt]

I'm using Entity Framework. Here is my code to update data :

public bool UpdateProblem(Problem problem)
        {
            if (problem == null) {
                throw new ArgumentException("Cannot add a null entity");
            }

            MathHubModelContainer ctx = new MathHubModelContainer();
            ctx.Configuration.LazyLoadingEnabled = false;
            ctx.Configuration.ProxyCreationEnabled = false;

            DbEntityEntry attachtedEntrys = ctx.Entry(problem);
            // Find Currently Entity Entry in Context
            DbEntityEntry entry = ctx.Entry<Post>(problem);

            // if does not attatch yet.
            if (entry.State == EntityState.Detached)
            {
                // new entity here is wrapped by proxy
                Problem attachedProblem = ctx.Set<Problem>().Find(problem.Id);
                if (attachedProblem != null)
                {
                    // get curently DBEntityEntry with AttachedProblem
                    DbEntityEntry attachtedEntry = ctx.Entry(attachedProblem);
                    attachtedEntry.CurrentValues.SetValues(problem);
                    attachtedEntry.State = EntityState.Modified;
                }
                else
                {
                    //entry.State = EntityState.Modified;
                    //entry.CurrentValues.SetValues(problem);
                    return false;
                }
            }
            else
            {
                // this entity has been attached to current context
                entry.CurrentValues.SetValues(problem);
                entry.State = EntityState.Modified;
            }

            ctx.SaveChanges();
            return true;
        }

Everything works fine (that I have checked database and I see all data has been saved successfully). But when I retrieve data :

DBContext ctx = new DBContext();
public Problem GetProblemById(int id)
        {

            return ctx.Posts.OfType<Problem>().FirstOrDefault(t => t.Id == id);
        }

Because I have used above DBContext object to get problem object, so, currently in that DBContext already contains one problem. so, when i retrieve problem, it will get old one, not the new object I have updated.

But if I changed to this :

public Problem GetProblemById(int id)
        {
            MathHubModelContainer ctx = new MathHubModelContainer();
            return ctx.Posts.OfType<Problem>().FirstOrDefault(t => t.Id == id);
        }

Everything works fine. So my question is :

How can i use just one DBContext object (not to create new one when calling), but still update data of object when another DBContext update it ?

Thanks :)

[Ketsuekiame]

If you want to use a single DbConext, then you must do just that all the way through the application.

It sounds like the DbContext has cached the previous version of the model and you've updated the model but bypassed the DbContext (so the cache hasn't updated)