Hi Paul,
This is a known issue in the ComboBoxBarItem and we have an open Bug report defect#666 on it. We will try our very best to address the same at the earliest. You could track the progress of this Bug fix at the link shown below :
Defect #666 - ComboBoxBarItem Editable property does not make ComboBoxBarItem editable.
We appreciate your feedback and thanks for your patience.
Regards,
Ebenezer.P