1. Create a project with RadGridView
2. Add a GridViewMultiComboBoxColumn
3. Attach to CellEditorInitialized event and try to handle PopupOpened event to change the popup size.

The SelectedValueChanged event is not fired when you select the current row after filtering.

Resolution: In Q1 2014 SP1 (2014.1.402) the first value from data source is selected by default and the event does not fire for already selected value.
If you select second or other value and after that select the first row, the SelectedValueChanged and SelectedIndexChanged are fired. 

ADD. RadMultiColumnComboBox - add ability to display focus cues when DropDownStyle = DropDownList

Using my two screenshots and values, note:
 1. Using Keyboard: I have 'A' selected and type a single 'W' to change my selection and hit enter. The next drop-down will still display at the width you see for the original A selection.  It will not be until the next drop-down that it resizes correctly.
 2. Using Mouse: I have 'A' selected and select the 'WWWW...." from the drop-down with my mouse.  The drop-down will appear correctly the next time.

RadMultiColumnComboBox should support suggest and suggest-append auto-complete modes when AutoFiltering is enabled.

Currently it is not possible to change the behavior of RadMultiColumnComboBox when using the AutoFilter mode. Check ticket ID 420127 for details.

Current row is selected in RadMultiColumnComboBox when the mouse's left button is released.

Set the AnimationEnabled property of RadCalendar and DropDownAnimationEnabled property in RadMultiColumnComboBox to false and there will be no effect.

When auto-filtering is applied to RadMultiColumnComboBox and mouse double click is performed over a row, the selected row is changed to another row.

FIX. RadMultiColumnComboBox. Setting the FormatString to a numeric column to some currency format and changing the column position results in displaying an invalid currency symbol.

When you select a row by pressing the left mouse button twice, you will select a wrong row if RadMultiColumnComboBox has filter applied.

This feature request refers to implementation of an AutoComplete mode for RadMultiColumnComboBox.

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.

If value member's column is not included in EditorControl (the grid) SelectedValue property always returns null.

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'"

radMultiColumnComboBox €“ set AutoFilter to be true and apply filter to radMultiColumnComboBox. Apply the filter in this way so no result is displayed in the drop down. Try to open the drop down and you will see that you cannot.

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.

TextChanged event of RadMultiColumnComboBox is not fired on many occasions.