datagridview multiple comboboxdropdowns across row....nasty bug...

My example inventory datagrid has four visible columns:

The first is just a text description, the second is a a Room, the
third is a list of items in the selected room, and the last is the final disposition
of the item in the room (Sell, Keep, or Throw_Away).

Columns Room, Item and Dispostion are datagridcomboboxes.

Items available to pick are determined by the selectedvaluechanged event of the Room
datagridcombobox.   It calls a function UpdateDisplayedItemListForRow().



When adding a new row, the user fills in the description, then picks a room by pressing a

key, in this example the room can be an Office or a Living Room.  So if the user presses

an "O" the Office selection is made and the user presses a tab key to move to the Items

column.   The office can contain a lamp, a desk, or a table.  So on the items column the user presses an L and the Lamp item is displayed.  Finally the user presses the tab key to move to the Disposition column.

This is where I am having trouble. Sometimes it works great, but at other times pressing

the tab key makes the Lamp entry vanish and leaves the Item column blank again!  I cannot

determine any rhyme or reason for this behavior, nor can I figure out where to put
a breakpoint to catch the problem.  (Although it is much less likely to happen when I am

debugging.)

The code is attached.  Can someone please help me figure out what I am doing to cause

this nasty bug and what I can do to squash it?  Please advise.

Thanks in advance.

Private Sub DataGridViewCommands_EditingControlShowing(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles DataGridViewCommands.EditingControlShowing

        Dim cbItem As ComboBox
        Dim cbdisp As ComboBox
        Dim cbrm As ComboBox

        Select Case Me.DataGridViewDescriptions.CurrentCell.ColumnIndex
            Case 0 'ROOMS
                cbrm = TryCast(e.Control, ComboBox)
                If cbrm Is Nothing Then
                    Exit Sub
                End If
                cbrm.Name = "ComboBoxRooms"

                RemoveHandler cbrm.SelectedValueChanged, New EventHandler(AddressOf gen_SelectionChanged)
                AddHandler cbrm.SelectedValueChanged, New EventHandler(AddressOf gen_SelectionChanged)
             

            Case 1   'ItemS
                cbItem = TryCast(e.Control, ComboBox)
                If cbItem Is Nothing Then
                    Exit Sub
                End If
                cbItem.Name = "ComboBoxItems"
               
                RemoveHandler cbItem.SelectedValueChanged, New EventHandler(AddressOf gen_SelectionChanged)
                AddHandler cbItem.SelectedValueChanged, New EventHandler(AddressOf gen_SelectionChanged)



            Case 2   'Dispostion
                cbdisp = TryCast(e.Control, ComboBox)
                If cbdisp Is Nothing Then
                    Exit Sub
                End If
                cbdisp.Name = "ComboBoxDisposition"
                
                RemoveHandler cbdisp.SelectedValueChanged, New EventHandler(AddressOf gen_SelectionChanged)
                AddHandler cbdisp.SelectedValueChanged, New EventHandler(AddressOf gen_SelectionChanged)
                
        End Select

    End Sub
    
  
    Public Sub gen_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs)

        Dim cmbBox As ComboBox = DirectCast(sender, ComboBox)
        Dim XC As DescriptionClass = ctrl.bs.Current

        If cmbBox.SelectedItem Is Nothing Then
            Exit Sub
        End If

        
        Select Case Me.DataGridViewDescriptions.CurrentCell.ColumnIndex
            Case 0
                XC.RoomCode = cmbBox.SelectedItem.RoomNo
                If Not ctrl.UpdateDisplayedItemListForRow(lex, XC.RoomCode) Then
                    MsgBox(lex.FullMessage, MsgBoxStyle.Critical, FormVeraMain.Text)
                End If
            Case 1
                XC.ItemCode = cmbBox.SelectedItem.ItemCode
                XC.X10Code = cmbBox.SelectedItem.X10Code
            Case 2
                XC.DispostionType = cmbBox.SelectedValue
                
        End Select

        If Not XC.NewRow Then
            XC.NextAction = "UPDATE"
        Else
            XC.NextAction = "ADD"
        End If

    End Sub


 Public Function UpdateDisplayedItemListForRow(ByRef lex As LastException, Optional ByVal int_roomcode As Integer = 0) As Boolean

        Dim retval As Boolean = True
        Dim dgr As DataGridViewRow = frm.DataGridViewCommands.CurrentRow
        Dim dgrcell As DataGridViewComboBoxCell
        Dim lst As List(Of ItemClass)

        dgrcell = dgr.Cells("Items")
        Dim roomcode As Integer

        If int_roomcode <> 0 Then
            roomcode = int_roomcode
        Else
            roomcode = dgr.Cells("RoomCode").Value
        End If


        If Not GetItems(lst, roomcode, lex) Then
            retval = False
        Else
            dgrcell.DisplayMember = "ItemName"
            dgrcell.ValueMember = "ItemCode"
            dgrcell.DataSource = lst
        End If
        Return retval

    End Function

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