While saving an object with navigation properties, the dbcontext saves two elements of same object about dbcontextscope HOT 1 OPEN

This is not an issue with this library but a misunderstanding from your side of how Entity Framework/ORMs work.

Because of its state management capabilities, when Entity Framework works with graphs, its entity state behavior doesn’t always align with your ideas of how it should work.
https://msdn.microsoft.com/en-us/magazine/dn166926.aspx

You probably have two options to rectify this mistake:

Option 1. Change your Client domain class

Add the following property:

[Column("Name of the VehicleID column on your CLient table here")
public int Vehicle_Id {get;set;}

In your code where you set
Client.vehicle = Vehicle;

Change it to
Client.Vehicle_id = Vehicle.Id;

Option 2. Attach the entity within your dbContextScope:

public void Save(Client client, Vehicle vehicle)
{
    using (var dbContextScope = _dbContextScopeFactory.Create())
    {
        //code that adds your Client to the context e.g.
        _clientRepository.Save(client);

        //Part you are interested in
        dbContextScope.DbContexts.Get<NameOfYourContext>().Vehicles.Attach(vehicle);
        dbContextScope.SaveChanges();
    }
}

from dbcontextscope.