Entity Framework Conflicting changes to the role of the Relationship have been Detected

Question

I have two objects that use a third in common and I have a problem in routine:

1) Creating a New Manufacturer

var fab = new Fabricante();
DBSet.Add(fab)   
//Sem SaveChanges

Then searching for the existing item and creating a new one, both of which use the same manufacturer not yet saved

var ItemProcesso = GetItem(1)
ItemProcesso.Fabricante = fab;

var adc = new Adicao()
adc.Fabricante = fab;
ItemProcesso.Adicao = adc;

Now before saving I need to know which fields are being changed from Then and that’s when the error occurs below:

var entryPro = Context.Entry(entity);

Error: Conflicting changes to the role 'Itemprocesso_fabricante_target' of the Relationship 'Portal.Infra.Data.Contexto.Itemprocesso_fabricante' have been Detected.

Now if I comment one of the 2 below the problem does not occur.

ItemProcesso.Fabricante = fab;
adc.Fabricante = fab;

NOTE: if I pass the Fabricanteid (object already saved) the problem does not occur

Does anyone know if there is any way to perform this operation without error? hint suggestions will also be welcome.