Issue with SwiftData inheritance (iOS 26)

Every time I insert a subclass (MYShapeLayer) into the model context, the app crashes with an error:

DesignerPlayground crashed due to fatalError in BackingData.swift at line 908. Never access a full future backing data - PersistentIdentifier(id: SwiftData.PersistentIdentifier.ID(backing: SwiftData.PersistentIdentifier.PersistentIdentifierBacking.managedObjectID(0xb2dbc55f3f4c57f2 x-coredata://B1E3206B-40DE-4185-BC65-4540B4705B40/MYShapeLayer/p1))) with Optional(A6CA4F89-107F-4A66-BC49-DD7DAC689F77)`

struct ContentView: View {
  
  @Environment(\.modelContext) private var modelContext
  
  @Query private var designs: [MYDesign]
  
  var layers: [MYLayer] {
    designs.first?.layers ?? []
  }
  
  var body: some View {
    NavigationStack {
      List {
        ForEach(layers) { layer in
          Text(layer.description)
        }
      }
      .onAppear {
        let design = MYDesign(title: "My Design")
        modelContext.insert(design)
        try? modelContext.save()
      }
      .toolbar {
        Menu("Add", systemImage: "plus") {
          Button(action: addTextLayer) {
            Text("Add Text Layer")
          }
          
          Button(action: addShapeLayer) {
            Text("Add Shape Layer")
          }
        }
      }
    }
  }
   
  private func addTextLayer() {
    if let design = designs.first {
      let newLayer = MYLayer(order: layers.count, kind: .text)
      newLayer.design = design
      modelContext.insert(newLayer)
      try? modelContext.save()
    }
  }
  
  private func addShapeLayer() {
    if let design = designs.first {
      let newLayer = MYShapeLayer(shapeName: "Ellipse", order: layers.count)
      newLayer.design = design
      modelContext.insert(newLayer)
      try? modelContext.save()
    }
  }
}

#Preview {
  ContentView()
    .modelContainer(for: [MYDesign.self, MYLayer.self, MYShapeLayer.self], inMemory: true)
}

@Model
final class MYDesign {
  
  var title: String = ""
  
  @Relationship(deleteRule: .cascade, inverse: \MYLayer.design)
  var layers: [MYLayer] = []
  
  init(title: String = "") {
    self.title = title
  }
  
}

@available(iOS 26.0, macOS 26.0, *)
@Model
class MYLayer {
  
  var design: MYDesign!
  
  var order: Int = 0
  
  var title: String = ""
  
  init(order: Int = 0, title: String = "New Layer") {
    self.order = order
    self.title = title
  }
  
}

@available(iOS 26.0, macOS 26.0, *)
@Model
class MYShapeLayer: MYLayer {
  
  var shapeName: String = ""
  
  init(shapeName: String, order: Int = 0) {
    self.shapeName = shapeName
    super.init(order: order)
  }
}