Breeze Sharp - does it support a navigation property that is a TBH descendant of the parent entity type being queried?

Question

Developing an n-tier Blazor app using Breeze.# and EF Core. I have two data model classes in a Table Per Hierarchy relationship. Here is a simplified form of the classes involved, but in reality there is far more going on.

Base class :

public partial class MfgBomHeader
{
    public virtual MfgBomHeader_Items? Specification { get; set; }
    
    [StringLength(10)]
    public string ActivityType { get; set; }
    [StringLength(30)]
    public string BomHeaderID { get; set; }
    [StringLength(10)]
    public string Revision { get; set; }
    [StringLength(10)]
    public string Type { get; set; }
}

Descendant class :

public partial class MfgBomHeader_Items : MfgBomHeader {}

In the DBContext the discriminator and relationship are specified :

modelBuilder.Entity<MfgBomHeader>(
    e =>
    {
        e.HasDiscriminator<string>(a => a.ActivityType)
        .HasValue<MfgBomHeader_Items>("");

        e.HasOne(c => c.Specification)
         .WithOne()
         .HasPrincipalKey<MfgBomHeader>(o => new { o.BomHeaderID, o.Revision, o.Type })
         .HasForeignKey<MfgBomHeader_Items>(b => new { b.BomHeaderID, b.Revision, b.Type }).IsRequired(false)
});

There are matching dto's, API clients and controllers for those data models, in the same manner as many others we have in the project. Here are the dto's :

public partial class MfgBomHeader : BaseEntity, IMfgBomHeader
{
    IMfgBomHeader_Items? IMfgBomHeader.Specification { get => Specification; set => Specification = (MfgBomHeader_Items)value; }
    
    public MfgBomHeader_Items? Specification
    {
        get { return GetValue<MfgBomHeader_Items?> (); }
        set { SetValue(value); }
    }
    public String ActivityType
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }
    public String BomHeaderID
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }
    public String Revision
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }
    public String Type
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }

}

public partial class MfgBomHeader_Items : BaseEntity, IMfgBomHeader_Items
{

    IMfgBomHeader_Items? IMfgBomHeader_Items.Specification { get => Specification; set => Specification = (MfgBomHeader_Items)value; }
    
    public MfgBomHeader_Items? Specification
    {
        get { return GetValue<MfgBomHeader_Items?> (); }
        set { SetValue(value); }
    }
    public String ActivityType
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }
    public String BomHeaderID
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }
    public String Revision
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }
    public String Type
    {
        get { return GetValue<String> (); }
        set { SetValue(value); }
    }

// I could also change this dto to instead inherit from the MfgBomHeader dto, but I get the same problem either way
}

So far so good.

But when the app starts up and Breeze initialises, Breeze examines its metadata and returns this error :

BaseApiClient.FetchMetadata: System.Exception: Unable to locate metadata resource for: https://localhost:44377/api/data/
 ---> System.Exception: Metadata errors encountered: 
EntityType metadata mismatch. EntityType: 'MfgBomHeader_Items:#Ops.Shared.Dto.Db'.  Metadata property: 'BaseEntityType'.  Client value: 'BaseEntity:#Breeze.Sharp',  Server value: 'MfgBomHeader:#Ops.Shared.Dto.Db'
   at Breeze.Sharp.MetadataStore.FetchMetadata(DataService dataService, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at Breeze.Sharp.MetadataStore.FetchMetadata(DataService dataService, CancellationToken cancellationToken)
   at Breeze.Sharp.EntityManager.FetchMetadata(CancellationToken cancellationToken, DataService dataService)
   at Breeze.Sharp.EntityManager.FetchMetadata(DataService dataService)

Breeze does not seem to understand that MfgBomHeader_Items inherits from MfgBomHeader, it just says "EntityType metadata mismatch",

(Actually, I have found that the models and dto's don't even work by themselves without the navigation property being involved, I get the same error that Breeze doesn't like that MfgBomHeader_Items inherits from MfgBomHeader).

So, my question is : does Breeze support this scenario?

Incidentally, if I change the type of the navigation property to MfgBomHeader rather than MfgBomHeader_Items then Breeze doesn't complain at startup, but instead I get a different problem when a Breeze query is performed on the base dto.
Breeze does not treat the navigation property entity as being a different thing from the base entity in the query, it simply copies the top level entity being returned and treats that as the navigation entity also (the base entity could have ActivityType = "abc" and the navigation entity should have ActivityType = "", but both have ActivityType = "abc")!!
If Breeze kept the two entities separate then I would simply use the type MfgBomHeader for the navigation property to keep things simple, but I feel I have to try the TPH approach to sidestep this problem.

EDIT 1 I was wrong about the dto MfgBomHeader_Items - if I make this dto inherit from the MfgBomHeader dto then I get further.

public partial class MfgBomHeader_Items : MfgBomHeader
{
}

I no longer receive the error :
"System.Exception: Metadata errors encountered: EntityType metadata mismatch".
Instead, with the navigation property set to the type MfgBomHeader_Items I now get this error when Breeze fetches its metadata :

System.NullReferenceException: Object reference not set to an instance of an object.
   at Breeze.Sharp.DataProperty.<>c__DisplayClass27_0.<set_DefaultValue>b__0(DataProperty dp)
   at Breeze.Sharp.Core.EnumerableFns.ForEach[T](IEnumerable`1 items, Action`1 action)
   at Breeze.Sharp.DataProperty.set_DefaultValue(Object value)
...etc...

So, now to resolve the NullReferenceException...