You are right about the EmptySelectionBoxTemplate. Since in editable mode RadComboBox can display only text, its control template does not contain the ContentPresenter, that displays EmptySelectionBoxTemplate in not editable mode. Probably we should thrown an exception when you have both EmptySelectionBoxTemplate and IsEditable=true, the same way like we throw when you set both DisplayMemberPath and ItemTemplate.
All the best,
the Telerik team
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