Selected Datagridview Cells Are Not Highlighted

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VB

DataGridView

I have a Datagridview with 5 columns, 3 of which are DatagridviewComboboxes with their style set to Dropdown. When I click on one of the DGVComboboxes it does not highlight blue (showing it is selected), though it does when I mouse over it. I can select the other two textbox cells and they highlight ok. When I select a whole row, the textbox cells highlight but the DGVCombobox cells do not.

Here is how I set the dropdown style for the DGVCombobox, in the DGV's EditingControlShowing event

Private Sub MediaContentsDataGrid_EditingControlShowing(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles MediaContentsDataGrid.EditingControlShowing
       'Allow user to enter new values for ALL DataGridViewComboBox controls in the DataGridView
       If (TypeOf e.Control Is DataGridViewComboBoxEditingControl) Then
           Dim cmb As DataGridViewComboBoxEditingControl = CType(e.Control, DataGridViewComboBoxEditingControl)
           If Not cmb Is Nothing Then
               cmb.DropDownStyle = ComboBoxStyle.DropDown

               ' add handler for comboboxes to limit their text length
               AddHandler cmb.KeyPress, AddressOf ContentsDataGridViewComboBoxColumn_KeyPress_MaxLength
           End If
       End If
   End Sub

The DGV as a whole functions fine, and I can use the DGVCombobox cells and even select them, they just don't highlight and appear selected (which is causing user confusion.)