No nested results in Entity Framework Core

i have a strange behavior in C# with EF It's a .NET Core project with EF Core 1.1.0

"Microsoft.EntityFrameworkCore.SqlServer": "1.1.0",
"Microsoft.EntityFrameworkCore.Tools": "1.1.0-preview4-final",

I've created two Models, "User" and "Group"

 public class User
 {
    public int Id { get; set; }
    public string name { get; set; }
    public string lastName { get; set; }

    public List<Group> Groups { get; set; }
 }

 public class Group
 {
    public int Id { get; set; }
    public string groupName { get; set; }
    public virtual User User { get; set; }
 }

The result schould give me a User with a list of his groups.

Now the strange part:

Result comes back from DB, i look into allUser, Groups are Null

I take a look into the context to see the Groups

Groups are filled:

Now i look again into allUser Result and magically the Group is filled inside every User item.

Groups are filled inside User:

I really appreciate any help!!