Why are some navigation properties lost through projection?

Question

I want to retrieve some data and use it in a new form that fits my use case. Because of the amount of data aswell as the data model eager loading is the prefered and faster way. Through this i stumbled upon something I can't explain.

The following is a simplified example:

Enitities

public class Car 
{
   public int Id { get; set; }

   public bool Deleted { get; set; }

   public string Name { get; set; }

   public virtual Engine Engine { get; set; }
   
   public virtual List<Tire> Tires { get; set; }
}

public class Engine
{
   public int Id { get; set; }   

   public string Name { get; set; }

   public int PS { get; set; }
}

public class Tire
{
   public int Id { get; set; }

   public string Name { get; set; }

   public int Profile { get; set; }
}

---

Code

var cars = DbContext.Current.Cars
                        .Include(c => c.Engine)
                        .Include(c => c.Tires)
                        .Where(c => !c.Deleted)
                        .Select(c => new {
                                      Car = c,
                                      TireIds = c.Tires.Select(t => t.Id)})
                        .ToList();

When I am trying to access the Engine later on it is not included and needs to be reloaded from the database which is expensive. Nevertheless the tires-Collection is present.

If I am doing the following, the engine is included later on.

Code

var cars = DbContext.Current.Cars
                        .Include(c => c.Engine)
                        .Include(c => c.Tires)
                        .Where(c => !c.Deleted)
                        .ToList();

var carsAndTires = cars.Select(c => new { Car = c, TireIds = c.Tires.Select(t => t.Id)}).ToList();