Entity Framework Conflicting changes to the role of the relationship have been detected

I have 2 objects that use a third party in common and I have a problem in the 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 ItemProcess then and it is at that moment that the error below occurs:

var entryPro = Context.Entry(entity);

Error: Conflicting changes to the role 'Producer_Product_Target' of the relationship 'Portal.Inf.Data.Context.ProviderItem' has been detected.

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

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

NOTE: If I pass the ManufacturerId (object already saved) the problem does not occur

Does anyone know if there is any way to perform this operation without error? Tip suggestions are also welcome.