Is it posted before?
            comboBox1.ValueMember = "baId";
            comboBox1.DisplayMember = "baName";
            comboBox1.DataSource = list;   //<--list of au
            comboBox1.DataBindings.Add("SelectedItem", au, "baAddress");
this line cause a no session exception. I think it is affected by first 2 lines. Bindings codes need to access related attributes on au instead of the one in the list. Though this access seems not necessary with the 'list' already set.

The baAddress is an attribute on au with lazy load, itself is a class.

Equals(object obj) on class of baAddress, is overrided for  binding the same obj.

Remove lazy load could be a choice. What other ideas?

agree. grow step by step.
What I have done in steps:
  1, all logic in the view, only for trial;
  2, have a clean view and move others to the mediator;
  3, have a clean mediator again, move others like database access to proxy;
  4, then at last using a command for a complex situation.
I was not sure using these in different situations at the beginning. But having in my mind that step 4 costs the most. And I need to confirm my thought, which this post does.
Cheers