When copy the RadMultiColumnComboBox control it pastes the underling grid as a separate control. Workaround: Place the RadMultiColumnComboBox on a UserControl, and introduce the desired settings there. Then reuse the user control in your forms.
When RadGridView is unbound and you try to create the columns for the RadMultiColumnComboBox manually, RadGridView throws an exception: "Cannot find column bound to 'field name'"
When you have a GridViewMultiComboBoxColumn in RadGridView, you can't set a custom size to the dropdown easily.
The RadMultiColumnComboBox control does not update its selection when the user types text in the text field. The expected behavior is that when the user types text and there is a databound item that matches the input, it should be selected. Otherwise, the current selection in the list should be cleared.