InvokeOperation entities become null - silverlight

Question

This is my method :-
[Invoke]
public List<FamilyEvent> GetFamilyEvents(int userId)
{
List<FamilyEvent> familyEvents = new List<FamilyEvent>();
int id = -1; //just to fool ria
//this is for birthday reminders.
var qry = ((from member in this.ObjectContext.TreeMembers.Where(m => m.UserId == userId && m.Birthdate == null)
select member.TreeMemberId).Except(from item in this.ObjectContext.FamilyEvents where item.ReminderType ==
FMT.Data.Web.Helpers.Global.FAMILY_EVENTS_REMINDERS.BIRTHDAY_REMINDER
select item.TreeMemberId));
var mainQry = from mainMember in this.ObjectContext.TreeMembers
where qry.Contains(mainMember.TreeMemberId)
select mainMember;
foreach (var item in mainQry)
{
FamilyEvent familyEvent = new FamilyEvent
{
FamilyEventId = id--,
TreeMemberId = item.TreeMemberId,
RelatedTreeMemberId = -1,
ReminderType = FMT.Data.Web.Helpers.Global.FAMILY_EVENTS_REMINDERS.BIRTHDAY_REMINDER
};
familyEvent.TreeMember = item;
familyEvents.Add(familyEvent);
}
//this is for anniversary events
qry = ((from member in this.ObjectContext.TreeMembers.Where(m => m.UserId == userId && m.RelationId == (short)Relations.Partner)
select member.TreeMemberId).Except(from item in this.ObjectContext.FamilyEvents where item.ReminderType == FMT.Data.Web.Helpers.Global.FAMILY_EVENTS_REMINDERS.ANNIVERSARY_REMINDER
select item.TreeMemberId));
mainQry = from mainMember in this.ObjectContext.TreeMembers.Include("RelatedTreeMember")
where qry.Contains(mainMember.TreeMemberId)
select mainMember;
foreach (var item in mainQry)
{
FamilyEvent familyEvent = new FamilyEvent
{
TreeMemberId = item.TreeMemberId,
TreeMember = item,
RelatedTreeMemberId = item.RelatedTreeMemberId,
ReminderType = FMT.Data.Web.Helpers.Global.FAMILY_EVENTS_REMINDERS.ANNIVERSARY_REMINDER
};
familyEvent.RelatedTreeMember = item.RelatedTreeMember;
familyEvents.Add(familyEvent);
}
return familyEvents;
}
As you can see i programmatically populate the entities and populate it. When i put breakpoint on return familyEvents, i can see the correct data. However on client side, the TreeMember and RelatedTreeMember value become null. Why is it so? If i do not use [Invoke] and instead use [Query] it works, but i need Invoke in my case.