Hello,

That is weird - I tried to reproduce the same problem (using latest release - 2008.3) and was not able to - in my case everything worked as expected. Here is my setup and and a screenshot of what I am getting

    <igtbl:UltraWebGrid ID="UltraWebGrid1" runat="server"
        DataSourceID="AccessDataSource1" Height="200px" Width="325px" >
        <Bands>
            <igtbl:UltraGridBand>
                <Columns>
                    <igtbl:UltraGridColumn BaseColumnName="RequiredDate" DataType="System.DateTime"  Format="hh:mm"
                        IsBound="True" Key="RequiredDate" Type="Custom" EditorControlID="WebDateTimeEdit1">
                        <Header Caption="RequiredDate">
                        </Header>
                    </igtbl:UltraGridColumn>
                    <igtbl:UltraGridColumn BaseColumnName="ShippedDate" DataType="System.DateTime"
                        IsBound="True" Key="ShippedDate">
                        <Header Caption="ShippedDate">
                            <RowLayoutColumnInfo OriginX="1" />
                        </Header>
                        <Footer>
                            <RowLayoutColumnInfo OriginX="1" />
                        </Footer>
                    </igtbl:UltraGridColumn>
                    <igtbl:UltraGridColumn BaseColumnName="ShipName" IsBound="True" Key="ShipName">
                        <Header Caption="ShipName">
                            <RowLayoutColumnInfo OriginX="2" />
                        </Header>
                        <Footer>
                            <RowLayoutColumnInfo OriginX="2" />
                        </Footer>
                    </igtbl:UltraGridColumn>
                </Columns>
                <AddNewRow View="NotSet" Visible="NotSet">
                </AddNewRow>
            </igtbl:UltraGridBand>
        </Bands>
        <DisplayLayout AllowColSizingDefault="Free" AllowColumnMovingDefault="OnServer"
            AllowDeleteDefault="Yes" AllowSortingDefault="OnClient"
            AllowUpdateDefault="Yes" BorderCollapseDefault="Separate"
            HeaderClickActionDefault="SortMulti" Name="UltraWebGrid1"
            RowHeightDefault="20px" RowSelectorsDefault="No"
            SelectTypeRowDefault="Extended" StationaryMargins="Header"
            StationaryMarginsOutlookGroupBy="True" TableLayout="Fixed" Version="4.00"
            ViewType="OutlookGroupBy">
            <FrameStyle BackColor="Window" BorderColor="InactiveCaption"
                BorderStyle="Solid" BorderWidth="1px" Font-Names="Microsoft Sans Serif"
                Font-Size="8.25pt" Height="200px" Width="325px">
            </FrameStyle>
            <Pager MinimumPagesForDisplay="2">
                <PagerStyle BackColor="LightGray" BorderStyle="Solid" BorderWidth="1px">
                <BorderDetails ColorLeft="White" ColorTop="White" WidthLeft="1px"
                    WidthTop="1px" />
                </PagerStyle>
            </Pager>
            <EditCellStyleDefault BorderStyle="None" BorderWidth="0px">
            </EditCellStyleDefault>
            <FooterStyleDefault BackColor="LightGray" BorderStyle="Solid" BorderWidth="1px">
                <BorderDetails ColorLeft="White" ColorTop="White" WidthLeft="1px"
                    WidthTop="1px" />
            </FooterStyleDefault>
            <HeaderStyleDefault BackColor="LightGray" BorderStyle="Solid"
                HorizontalAlign="Left">
                <BorderDetails ColorLeft="White" ColorTop="White" WidthLeft="1px"
                    WidthTop="1px" />
            </HeaderStyleDefault>
            <RowStyleDefault BackColor="Window" BorderColor="Silver" BorderStyle="Solid"
                BorderWidth="1px" Font-Names="Microsoft Sans Serif" Font-Size="8.25pt">
                <Padding Left="3px" />
                <BorderDetails ColorLeft="Window" ColorTop="Window" />
            </RowStyleDefault>
            <GroupByRowStyleDefault BackColor="Control" BorderColor="Window">
            </GroupByRowStyleDefault>
            <GroupByBox>
                <BoxStyle BackColor="ActiveBorder" BorderColor="Window">
                </BoxStyle>
            </GroupByBox>
            <AddNewBox Hidden="False">
                <BoxStyle BackColor="Window" BorderColor="InactiveCaption" BorderStyle="Solid"
                    BorderWidth="1px">
                    <BorderDetails ColorLeft="White" ColorTop="White" WidthLeft="1px"
                        WidthTop="1px" />
                </BoxStyle>
            </AddNewBox>
            <ActivationObject BorderColor="" BorderWidth="">
            </ActivationObject>
            <FilterOptionsDefault>
                <FilterDropDownStyle BackColor="White" BorderColor="Silver" BorderStyle="Solid"
                    BorderWidth="1px" CustomRules="overflow:auto;"
                    Font-Names="Verdana,Arial,Helvetica,sans-serif" Font-Size="11px" Height="300px"
                    Width="200px">
                    <Padding Left="2px" />
                </FilterDropDownStyle>
                <FilterHighlightRowStyle BackColor="#151C55" ForeColor="White">
                </FilterHighlightRowStyle>
                <FilterOperandDropDownStyle BackColor="White" BorderColor="Silver"
                    BorderStyle="Solid" BorderWidth="1px" CustomRules="overflow:auto;"
                    Font-Names="Verdana,Arial,Helvetica,sans-serif" Font-Size="11px">
                    <Padding Left="2px" />
                </FilterOperandDropDownStyle>
            </FilterOptionsDefault>
        </DisplayLayout>
    </igtbl:UltraWebGrid>
      
   
    <asp:AccessDataSource ID="AccessDataSource1" runat="server"
        DataFile="~/App_Data/Nwind.mdb"
        SelectCommand="SELECT [RequiredDate], [ShippedDate], [ShipName] FROM [Invoices]">
    </asp:AccessDataSource>   
   
    <igtxt:WebDateTimeEdit ID="WebDateTimeEdit1" runat="server" EditModeFormat="hh:mm">

Is there anything different in your setup?