ComboBox items are not accessible on the server-side when loading them on demand

ComboBox items loaded on demand using the ItemsRequested event handler or WebService do not exist on the server and cannot be accessed using the server-side FindItemByText / Value methods. SelectedItem and SelectedIndex properties are always Null / Nothing.
This is needed for speed (otherwise the combobox will not be that responsive upon each keypress if state information and ViewState were persisted).

The properties that are accessible on the server are: Text and SelectedValue.