CreateBindingSet<Target,Source> doesn't work well with the baseclass of the VM
## 🐛 Bug Report

I have a baseclass ComboboxInput and a Generic child class ComboboxInput<T>. In the VM we create a list of generic typed ComboboxInput's and in a TabeViewController cell we use a bindingset like:

```csharp
var set = this.CreateBindingSet<ComboboxView,ComboboxInput>()
set.bind(_combobox).For( c => c.LabelText).To(vm => vm.LabelText);
...
...
set.Applay();
```

this wil work fine for the labels en de selected items. but the list of combobox options are scattered over all the comboboxes. I'v tried to omit the fluent binding api here. This works for 90% but there the order of comboboxes are off. This means that I had an combobox order of "combobox1, combobox2, combobox3, combobox4" but without the use of a bindingSet I got "combobox1, combobox4, combobox2, combobox3". 

my code without BindingSets is as follow:

```csharp
var _combobox = new Comobox(); // used as an illustration to the combobox view

this.DelayBind(() =>  
{
    if(this.DataContext is ComboboxInput combobox)
    {
        _combobox.LabelText = combobox.LabelText;
        _combobox.Items = combobox.Items;
        _combobox.SelectedItem = combobox.SelectedItem;

        _combobox.PropertyChanged += (s, e) =>
        {
            switch(e.Propertyname)
            {
                  case "LabelText ":
                     combobox.LabelText = _combobox.LabelText;
                     break;
                  case "Items":
                     combobox.Items = _combobox.Items;
                     break;
                  case "SelectedItem":
                     combobox.SelectedItem = _combobox.SelectedItem;
                     break;
            }
        }
    }
});
```

### Expected behavior
I expect that the createBindingSet function should handle baseclasses properly. And I would know the did mashup the order of comboboxes in my "solution". It would also be nice to find a indepth demo about how the binding works because that way it would be easier to fix it myself.

### Reproduction steps

### Configuration

**Version:** 6.4.2

**Platform:** 
- [x] :iphone: iOS
- [ ] :robot: Android
- [ ] :checkered_flag: WPF
- [ ] :earth_americas: UWP
- [ ] :apple: MacOS
- [ ] :tv: tvOS
- [ ] :monkey: Xamarin.Forms
