Post History

I did not find the exact cause of your issue, but inserts should not be treated as updates. One way to do this is the following:

```c#
static void InsertPost(Post post)
{
    using var context = new BloggingContext();
    context.Posts.Add(post);
    context.SaveChanges();
}

var newPost = new Post
{
    BlogId = blog.BlogId,
    Title = "Goodbye World",
    Content = "Some content"
};

No need to use the navigation property, since we have the BlogId for the new post.
```

However, it is not recommended for the EF db contexts to leak models like this. As already noticed, it might lead to strange behavior, hard to debug and maintain software. 

I would split all operations into independent "use cases". The code would look like the following:

```c#
public static void Main()
{
	int blogId = SetupBlog();

	var posts = GetPosts(blogId);
	PrintPosts("Initial posts", posts);

	UpdateFirstPostTitle(blogId);
	PrintPosts("After editing", GetPosts(blogId));

	InsertPost(blogId);
	PrintPosts("After adding a new post", GetPosts(blogId));

	Remove(blogId);
}

static void PrintPosts(string header, IEnumerable<Post> posts)
{
	Console.WriteLine($"\n{header}\n{new string('=', header.Length)}");
	foreach (var post in posts)
	{
		Console.WriteLine($"{post.Title}: {post.Content}");
	}
}

static void Remove(int blogId)
{
	using var context = new BloggingContext();
	var blog = context.Blogs.Find(blogId);
	if (blog != null)
	{
		context.Remove(blog);
		context.SaveChanges();
	}
}

static int SetupBlog()
{
	using var context = new BloggingContext();

	var blog = new Blog { Url = "http://blogs.msdn.com/adonet" };
	blog.Posts.Add(new Post { Title = "Hello World", Content = "I wrote an app using EF Core!" });
	context.Add(blog);
	context.SaveChanges();

	return blog.BlogId;
}

static Post[] GetPosts(int blogId)
{
	using var context = new BloggingContext();
	return context.Posts.Where(p => p.BlogId == blogId).ToArray();
}

static void InsertPost(int blogId)
{
	using var context = new BloggingContext();

	var newPost = new Post
	{
		BlogId = blogId,
		Title = "Goodbye World",
		Content = "Some content"
	};

	context.Posts.Add(newPost);
	context.SaveChanges();
}

static void UpdateFirstPostTitle(int blogId)
{
	using var context = new BloggingContext();
	var post = context.Posts.First(p => p.BlogId == blogId);
	post.Title = "Hello World (edited)";
	context.SaveChanges();
}
```

Instead of pushing models around, we are working with ids and all the operations are clear and isolated.