[FlexGrid] FlexGridFilter not showing with custom CellFactory

Hi,

we have building a PoC with the FlexGrid component, but have run into an issue with the FlexGridFilter. We have added the FlexGridFilter in the XAML like this:

<c1:C1FlexGrid Grid.Row="1" x:Name="coGrid" c1:LicenseMode.Evaluation="True" HorizontalAlignment="Left" Margin="0,0,0,0" VerticalAlignment="Top" Height="Auto" Width="Auto" AllowResizing="Both" AutoComplete="True" ClipboardPasteMode="ExcludeHeader" ClipboardCopyMode="ExcludeHeader" AllowMerging="ColumnHeaders" ShowMarquee="True">
            <c1:C1FlexGridFilterService.FlexGridFilter>
                <c1:C1FlexGridFilter />
            </c1:C1FlexGridFilterService.FlexGridFilter>
        </c1:C1FlexGrid>

Which works great. Until we add a custom CellFactory, which makes the filter controls in the columns disappear. Is there an action we need to do in the CellFactory to enable the filter controls on the columns?