Custom ComboBox set Selected Value

I have a UI Customization with a custom dropdown combo.

I load this combobox during the EpiNotification event. It loads fine but does not show the default selected value.

When setting up the combobox, I set the EpiBinding = PartRev.myField_c

If I force the selected value after the data is loaded it causes the form to become dirty. WHich causes the form to call the BO Update method.

How do I set the default value after the combox is loaded?