Why Entity Framework replaces provided value with a new incremental value - asp.net-core-mvc

Question

I'm trying to work my way through a Dot Net Core MVC project, but I am facing a problem I couldn't solve.
And honestly, I didn't know what to search for.
The project is a simple vehicle registry,
Each vehicle has a Make, a Model, a some Features.
Here are the domain models:
public class Make
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Model> Models { get; set; }
public Make()
{
Models=new Collection<Model>();
}
}
public class Model
{
public int Id { get; set; }
public string Name { get; set; }
public Make Make { get; set; }
public int MakeId { get; set; }
public Model()
{
Make=new Make();
}
}
public class Feature
{
public int Id { get; set; }
public string Name { get; set; }
}
[Table(name:"VehicleFeatures")]
public class VehicleFeature
{
public int VehicleId { get; set; }
public int FeatureId { get; set; }
public Feature Feature { get; set; }
public Vehicle Vehicle { get; set; }
public VehicleFeature()
{
Feature=new Feature();
Vehicle=new Vehicle();
}
}
public class Vehicle
{
public int Id { get; set; }
public Model Model { get; set; }
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int ModelId { get; set; }
public ICollection<VehicleFeature> VehicleFeatures { get; set; }
public string ContactName { get; set; }
public string ContactPhone { get; set; }
public string ContactEmail { get; set; }
public DateTime LastUpdate { get; set; }
public bool IsRegistered { get; set; }
public Vehicle()
{
Model=new Model();
VehicleFeatures=new Collection<VehicleFeature>();
}
}
The problem is that when I send the following request to the corresponding controller, EF is replacing the provided value with a new incremental value.
The request I send:
{
"ModelId":10,
"VehicleFeatures":[
{"featureId":45},
{"featureId":46}
],
"ContactName":"Alice",
"ContactPhone":"1234",
"ContactEmail":"Alice#local",
"LastUpdate":"1980-01-01",
"IsRegistered":true
}
And this is what happens:
The controller receives correct values,
Correct values are added to the context,
And then suddenly all hell breaks loose.
This is the controller code:
[HttpPost]
public async Task<IActionResult> CreateVehicle([FromBody] Vehicle v)
{
context.Vehicles.Add(v);
await context.SaveChangesAsync();
return Ok(v.ModelId);
}
What am I missing here?