EF6 - Adding new associated child not populating Navigation Properties - entity-framework

Question

I have the following code which adds members to a parent group. The issue I'm running into is that the LAST member added to the PCSGroupMembers collection will not load it's navigation properties on demand. I have a set of 3 I've tried adding in various orders... the first 2 always work, the last one won't load the nav properties.
In the case below, you'll see 6 members total. The last 3 are the ones I just added in this request are the SAME IDS as the first 3 (unique key is groupid, memberid, startdate), so I know for sure there isn't an issue with a "bad FK" or similar. The first two of the new members are building out their nav properties, but that last one never does. Doesn't matter if I'm adding 2, 3, 4, etc. Last one never populates.
What seems REALLY odd to me is the PcsGroupID is an empty Guid on that last one even though it got added to the group via group.PcsGroupMembers.add(pcsMember) in the code below.
Edit: If you see the block labeled Hack, however, the real final member now has it's Nav properties. The faked temp member is then removed from the collection (and context) and everything magically works. So....WAT?
Code to add new members
//expire all existing members ([0..2] in this example)
group.PCSGroupMembers
.Where(m => m.EndDate == null)
.ToList().ForEach(m => {
m.EndDate = DateTime.Now.Date;
});
//add new members from request ([3..5] in this example)
foreach (PcsGroupMemberAddViewModel member in requestViewModel.Members) {
PCSGroupMember pcsMember = db.PCSGroupMembers.Create();
pcsMember.PCSSplitID = Guid.NewGuid();
pcsMember.ProjectProtocolID = member.ProjectProtocolID;
pcsMember.SplitAmount = member.Split;
pcsMember.IsPrimary = member.IsPrimary;
pcsMember.StartDate = DateTime.Now.Date;
group.PCSGroupMembers.Add(pcsMember);
}
Second to last (index 4)
Last Child (index 5)
Hack
var tempmember = db.PCSGroupMembers.Create();
//this Add seems to trigger the previous 'real' item to load it's Nav properties.... ???
group.PCSGroupMembers.Add(tempmember);
group.PCSGroupMembers.Remove(tempmember); //remove from collection
db.PCSGroupMembers.Remove(tempmember); //remove from context