How to resolve unexpected behavior in SwiftData LinkedList

I tried to practice SwiftData by creating a LinkedList. However, contrary to my expectations.

even though a.next == b

but b.next != nil, b.next == a. Why is that?

@Environment(\.modelContext) private var modelContext
@Query private var items: [Item]
Button {
        var a = Item(value: 0)
        var b = Item(value: 1)
        a.next = b
        modelContext.insert(a)
      } label: {
        Text("+++")
      }
@Model
final class Item {
    var value: Int
    weak var next: Item?
    
    init(value: Int, next: Item? = nil) {
        self.value = value
        self.next = next
    }
}

this is whole code

import SwiftUI
import SwiftData

struct ContentView: View {
  @Environment(\.modelContext) private var modelContext
  @Query private var items: [Item]

  var body: some View {
    ZStack {
      VStack {
        ForEach(items){item in
          Button {
            modelContext.delete(item)
          } label: {
            Text(String(item.value))
          }
        }
      }
    }
    VStack {
      Button {
        var a = Item(value: 0)
        var b = Item(value: 1)
        a.next = b
        modelContext.insert(a)
//        modelContext.insert(b)
//        let fetch = FetchDescriptor<Item>(
//          predicate: #Predicate{$0.value == 0}
//        )
//        let data = try! modelContext.fetch(fetch)
//        data[0].next = b
      } label: {
        Text("+++")
      }
      Button {
        for i in items {
          modelContext.delete(i)
        }
      } label: {
        Text("---")
      }
      Button {
        for i in items {
          print(i.value)
          print(i.next)
        }
      } label: {
        Text("Print")
      }
    }
  }
}

#Preview {
  ContentView()
    .modelContainer(for: Item.self, inMemory: true)
}