Combobox - reference not being set

I’ve come across this strange little quoible.
It’s possibly just just the way I’ve been trying to use it, but it still seems odd to me

If you have a ComboBox which you are databinding to using an object, like:

<ComboBox SelectedItem=”{Binding Path=Market}” />
Where Market is a reference to another object

If you fail to initialise the object , Market in this case, the combobox won’t do it!

Obviously, the circumstances in a LOB application are more complex than the simple example above, but it does seem bizarre behaviour.