EF 4.3 (Code First) - Custom ICollection Fails to catch new items - entity-framework

Question

This is in reference to the question I asked regarding how to determine when items are added to the virtual ICollection property. As suggested, I have created a custom collection which inherits from Collection as shown below
public class EntityCollection<T> : Collection<T>
{
protected override void InsertItem(int index, T item)
{
base.InsertItem(index, item);
}
}
This is being used as
public class DbAppointment
{
public DbAppointment()
{
exceptionOcurrences = new EntityCollection<DbExceptionOcurrence>();
}
public virtual int AppointmentId { get; set; }
public virtual string Subject { get; set; }
public virtual string Body { get; set; }
public virtual DateTime Start { get; set; }
public virtual DateTime End { get; set; }
private ICollection<DbExceptionOcurrence> exceptionOcurrences;
public virtual ICollection<DbExceptionOcurrence> ExceptionOcurrences
{
get { return exceptionOcurrences; }
set { exceptionOcurrences = value; }
}
}
The problem is the only time the overridden InsertItem method seems to get called is if I initialise the database with a custom initialiser (example code below) and override the seed method!! What am I doing wrong?
Cheers
Abs
public class ContextInitializer : DropCreateDatabaseAlways<Context>
{
protected override void Seed(Context context)
{
new List<DbAppointment>
{
new DbAppointment{ Subject = "hello", Body="world", Start=DateTime.Now, End=DateTime.Now.AddMinutes(30)},
}.ForEach(a => context.Appointments.Add(a));
new List<DbExceptionOcurrence>
{
new DbExceptionOcurrence{ExceptionDate=DateTime.Now}
}.ForEach(eo => context.ExceptionOcurrences.Add(eo));
base.Seed(context);
}
}