Issue is reproducible with the following code:
        <telerik:RadHtmlChart runat="server" ID="ColumnChart1" Width="600px" Height="400px">
            <PlotArea>
                <Series>
                    <telerik:ColumnSeries Name="Product 1">
                        <SeriesItems>
                            <telerik:CategorySeriesItem Y="10" />
                            <telerik:CategorySeriesItem Y="8" />
                        </SeriesItems>
                        <LabelsAppearance Position="Center"></LabelsAppearance>
                    </telerik:ColumnSeries>
                </Series>
            </PlotArea>
        </telerik:RadHtmlChart>
For the time being you can change the labels position from "Center" to "OutsideEnd".