For the time being the following workaround can be used:

JavaScript:

    <script>
        function pageLoad() {
            var chart = $find("<%=RadHtmlChart1.ClientID%>");
            chart._chartObject.options.series[0].missingValues = "Gap";
            chart.repaint();
        }
    </script>
ASPX:

        <telerik:RadHtmlChart ID="RadHtmlChart1" runat="server">
            <PlotArea>
                <Series>
                    <telerik:LineSeries MissingValues="Gap">
                        <SeriesItems>
                            <telerik:CategorySeriesItem Y="30" />
                            <telerik:CategorySeriesItem Y="10" />
                            <telerik:CategorySeriesItem />
                            <telerik:CategorySeriesItem Y="30" />
                        </SeriesItems>
                    </telerik:LineSeries>
                </Series>
            </PlotArea>
        </telerik:RadHtmlChart>

The workaround is to set <MarkersAppearance Visible="false"  />.

Code that reproduces the issue:

<telerik:RadHtmlChart runat="server" ID="RadHtmlChartColumnGender" Transitions="true" Width="150" Height="300">
			<PlotArea>
				<Series>
					<telerik:ColumnSeries Name="Male" Stacked="true" StackType="Stack100">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="69" />
						</SeriesItems>
					</telerik:ColumnSeries>
					<telerik:ColumnSeries Name="Female" Stacked="true" StackType="Stack100">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="3" />
						</SeriesItems>
					</telerik:ColumnSeries>
				</Series>
				<YAxis NarrowRange="false"></YAxis>
			</PlotArea>

		</telerik:RadHtmlChart>

Workaround:

		<script>
			function pageLoad() {
				var kendoChart = $find("RadHtmlChartColumnGender").get_kendoWidget();
				var valueAxis = kendoChart.options.valueAxis;
				valueAxis.narrowRange = false;
				$find("RadHtmlChartColumnGender").setOptions({valueAxis: valueAxis});
			}
		</script>

               <script>
			function chartLoad() {
				$find("RadHtmlChart2").get_kendoWidget().setOptions({
					legend: {
						position: "top",
						width: 162,
						height: 88,
						orientation: "vertical"
					}
				})
			}
		</script>
		<telerik:RadHtmlChart ID="RadHtmlChart2" runat="server" Width="350" Height="350">
			<ClientEvents OnLoad="chartLoad" />
			...
		</telerik:RadHtmlChart>

The CSS styles of the selection hint of the navigator in HtmlChart are not applied correctly in a data navigation scenario.

The workaround is to override the styles that you need like this:
        .k-navigator-hint .k-tooltip {
            border: 2px solid red !important;
            color: #000 !important;
        }

Hover over first legend item highlights all chart sections for donut chat type.
Hover over the rest of the legend items doesn't highlight the corresponding section of the donut chart.

JavaScript workaround:
		<telerik:RadHtmlChart runat="server" ID="LineChart" Width="800" Height="500" Transitions="true">
			<PlotArea>
				<Series>
					<telerik:LineSeries Name="Week 15" ZIndex="0">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="15" />
							<telerik:CategorySeriesItem />
							<telerik:CategorySeriesItem Y="71" />
							<telerik:CategorySeriesItem Y="93" />
							<telerik:CategorySeriesItem Y="43" />
							<telerik:CategorySeriesItem Y="23" />
						</SeriesItems>
					</telerik:LineSeries>
				</Series>
			</PlotArea>
		</telerik:RadHtmlChart>
		<script>
			kendo.dataviz.LineChart.fn.animationPoints = function () {
				var series = this.seriesOptions;
				var points = [];
				var seriesPoints;
				var pointsIdx, idx;
				for (idx = 0; idx < series.length; idx++) {
					if (series[idx].markers.visible) {
						seriesPoints = this.seriesPoints[idx];
						for (pointsIdx = 0; pointsIdx < seriesPoints.length; pointsIdx++) {
							if (seriesPoints[pointsIdx] != null) {
								points.push(seriesPoints[pointsIdx].marker);
							}
						}
					}
				}
				return points.concat(this._segments);
			}
		</script>

For the time being you can use the following JavaScript workaround:

		<telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" Width="600" Height="300">
			<PlotArea>
				<Series>
					<telerik:LineSeries Name="series 1">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="30" />
							<telerik:CategorySeriesItem Y="10" />
							<telerik:CategorySeriesItem Y="25" />
							<telerik:CategorySeriesItem Y="20" />
						</SeriesItems>
					</telerik:LineSeries>
				</Series>
				<XAxis MinValue="1">
				</XAxis>
			</PlotArea>
		</telerik:RadHtmlChart>
		<script>

                       //JavaScript workaround

			function isNumber(val) {
				return typeof val === "number" && !isNaN(val);
			}


			var dataviz = kendo.dataviz,
				inArray = dataviz.inArray,
				deepExtend = kendo.deepExtend,
				math = Math,
				AREA = "area",
				VERTICAL_AREA = "verticalArea",
				VERTICAL_LINE = "verticalLine",
				LINE = "line";

			kendo.dataviz.CategoricalPlotArea.fn.filterSeries = function (currentSeries, categoryAxis) {
				var range = categoryAxis.totalRangeIndices();
				var justified = categoryAxis.options.justified;
				var outOfRangePoints = inArray(currentSeries.type, [LINE, VERTICAL_LINE, AREA, VERTICAL_AREA]);
				var categoryIx;

				range.min = isNumber(categoryAxis.options.min) ? math.floor(range.min) : 0;
				range.max = isNumber(categoryAxis.options.max) ? (justified ? math.floor(range.max) + 1 : math.ceil(range.max)) : currentSeries.data.length;

				currentSeries = deepExtend({}, currentSeries);

				if (outOfRangePoints) {
					var minCategory = range.min - 1;
					var srcCategories = categoryAxis.options.srcCategories || [];
					if (minCategory >= 0 && minCategory < currentSeries.data.length) {
						categoryIx = minCategory;
						currentSeries._outOfRangeMinPoint = {
							item: currentSeries.data[categoryIx],
							category: srcCategories[categoryIx],
							categoryIx: -1
						};
					}

					if (range.max < currentSeries.data.length) {
						categoryIx = range.max;
						currentSeries._outOfRangeMaxPoint = {
							item: currentSeries.data[categoryIx],
							category: srcCategories[categoryIx],
							categoryIx: range.max - range.min
						};
					}
				}

				categoryAxis._seriesMax = math.max(categoryAxis._seriesMax || 0, currentSeries.data.length);

				currentSeries.data = (currentSeries.data || []).slice(range.min, range.max);

				return currentSeries;
			}
		</script>

The workaround is to convert the color names to HEX, for example through the following HexConverter() method:
ASPX:

        <telerik:RadClientExportManager runat="server" ID="RadClientExportManager1">
        </telerik:RadClientExportManager>
        <telerik:RadButton ID="RadButton1" runat="server" OnClientClicked="exportRadHtmlChart" Text="Export RadHtmlChart to PDF" AutoPostBack="false" UseSubmitBehavior="false"></telerik:RadButton>
        <telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" Width="600" Height="400">
            <PlotArea>
                <Series>
                    <telerik:ColumnSeries Name="Series 1" DataFieldY="myValues" ColorField="Color">
                    </telerik:ColumnSeries>
                </Series>
            </PlotArea>
        </telerik:RadHtmlChart>
        <script>
            var $ = $telerik.$;
            function exportRadHtmlChart() {
                $find('<%=RadClientExportManager1.ClientID%>').exportPDF($(".RadHtmlChart"));
            }
        </script>

C#:

    protected void Page_Load(object sender, EventArgs e)
    {
        DataTable dt = GetData();

        for (int i = 0; i < dt.Rows.Count; i++)
        {
            //Not all Color Names can be exported
            // dt.Rows[i]["Color"] = ColorTranslator.ToHtml(GetColor(i));

            //Convert colors to HEX works properly
            dt.Rows[i]["Color"] = HexConverter(GetColor(i));
        }
        RadHtmlChart1.DataSource = dt;
        RadHtmlChart1.DataBind();
    }

    public static DataTable GetData()
    {
        DataTable dt = new DataTable("ChargeData");
        dt.Columns.Add("myValues", typeof(int));
        dt.Columns.Add("Color", typeof(string));


        dt.Rows.Add(11, "");
        dt.Rows.Add(12, "");
        dt.Rows.Add(13, "");
        dt.Rows.Add(14, "");
        dt.Rows.Add(15, "");
        dt.Rows.Add(16, "");
        dt.Rows.Add(17, "");
        dt.Rows.Add(18, "");
        dt.Rows.Add(19, "");
        dt.Rows.Add(20, "");
        return dt;
    }

    public static String HexConverter(System.Drawing.Color c)
    {
        return "#" + c.R.ToString("X2") + c.G.ToString("X2") + c.B.ToString("X2");
    }

    public static Color GetColor(int index)
    {
        return colors[index % colors.Length];
    }

    public static readonly Color[] colors =
    {
        Color.Orange,
        Color.Violet,
        Color.MediumSeaGreen,
        Color.HotPink,
        Color.Black,
        Color.DarkGoldenrod,
        Color.DarkMagenta,
        Color.Chocolate,
        Color.DarkOliveGreen,
        Color.DarkTurquoise
    };

Currently when RadHtmlChart is placed inside  RadSplitter with RadSlidingZone a JavaScript error is thrown when the following conditions are met:

1.RadHtmlChart doesn't have its width property set

2.The position of the RadHtmlChart's legend is changed in the codebehind

The workaround is to set the width property of the chart.

For the time being the reversed properties can be set through the kendo widget:
		<script>
			function pageLoad(sender, args) {

				var radarChart = $find('<%=RadarLineChart.ClientID%>').get_kendoWidget();
				var polarChart = $find('<%=PolarAreaChart.ClientID%>').get_kendoWidget();


				radarChart.options.valueAxis.reverse = true;
				polarChart.options.yAxis.reverse = true;


				radarChart.options.categoryAxis.reverse = true;
				polarChart.options.xAxis.reverse = true;

				radarChart.redraw();
				polarChart.redraw();
			}
		</script>

		<telerik:RadHtmlChart runat="server" ID="RadarLineChart" Width="345" Height="345">
			<PlotArea>
				<XAxis Reversed="true">
					<Items>
						<telerik:AxisItem LabelText="January"></telerik:AxisItem>
						<telerik:AxisItem LabelText="February"></telerik:AxisItem>
						<telerik:AxisItem LabelText="March"></telerik:AxisItem>
						<telerik:AxisItem LabelText="April"></telerik:AxisItem>
						<telerik:AxisItem LabelText="May"></telerik:AxisItem>
					</Items>
				</XAxis>
				<YAxis Reversed="true">
				</YAxis>
				<Series>
					<telerik:RadarLineSeries Name="Avg Low" MissingValues="Gap">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="1000"></telerik:CategorySeriesItem>
							<telerik:CategorySeriesItem Y="8000"></telerik:CategorySeriesItem>
							<telerik:CategorySeriesItem Y="11000"></telerik:CategorySeriesItem>
							<telerik:CategorySeriesItem Y="13000"></telerik:CategorySeriesItem>
							<telerik:CategorySeriesItem Y="12000"></telerik:CategorySeriesItem>
						</SeriesItems>
					</telerik:RadarLineSeries>
				</Series>
			</PlotArea>
		</telerik:RadHtmlChart>

		<telerik:RadHtmlChart runat="server" ID="PolarAreaChart" Width="345" Height="345">
			<PlotArea>
				<XAxis Reversed="true">
				</XAxis>
				<YAxis Reversed="true">
				</YAxis>
				<Series>
					<telerik:PolarAreaSeries Name=">12.3 knots">
						<SeriesItems>
							<telerik:PolarSeriesItem Angle="125" Radius="2.4"></telerik:PolarSeriesItem>
							<telerik:PolarSeriesItem Angle="138" Radius="7.5"></telerik:PolarSeriesItem>
							<telerik:PolarSeriesItem Angle="152" Radius="8.3"></telerik:PolarSeriesItem>
							<telerik:PolarSeriesItem Angle="166" Radius="4.3"></telerik:PolarSeriesItem>
						</SeriesItems>
					</telerik:PolarAreaSeries>
				</Series>
			</PlotArea>
		</telerik:RadHtmlChart>

The current behavior of the RadHtmlChart preserves only the bound datasource, however it doesn't store programmatically added series items after a postback.

The workaround is instead of creating and adding series items programmatically, create a datatable and pass it as a datasource to the chart. For example:
ASPX:
<telerik:RadHtmlChart runat="server" ID="RadHtmlChart1" Width="600px" Height="400px">
</telerik:RadHtmlChart>
C#:
protected void Page_Load(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.Add("id");
    dt.Columns.Add("xValues");
    dt.Columns.Add("yValues");
    for (int i = 0; i < 5; i++)
    {
        dt.Rows.Add(i, (10 + i).ToString() + " Apr", 20 + i);
    } 
    ScatterLineSeries sls1 = new ScatterLineSeries();
    sls1.LabelsAppearance.DataFormatString = "{0:d}";
    sls1.DataFieldX = "xValues";
    sls1.DataFieldY = "yValues";
  
    RadHtmlChart1.PlotArea.Series.Add(sls1);
    RadHtmlChart1.DataSource = dt;
    RadHtmlChart1.DataBind();
}

When data-bound categorical series has zeros in the x-axis labels they are parsed and the zeros disappear. For example:
ASPX:

            <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
            <telerik:RadHtmlChart runat="server" ID="Radhtmlchart1">
                <PlotArea>
                    <Series>
                        <telerik:ColumnSeries DataFieldY="Score1"></telerik:ColumnSeries>
                   </Series>

                   <XAxis DataLabelsField="Student">
                    </XAxis>
                </PlotArea>
            </telerik:RadHtmlChart>

C#:

    protected void Page_Load(object sender, EventArgs e)
    {
        Radhtmlchart1.DataSource = GetData();
        Radhtmlchart1.DataBind();
    }
    protected DataTable GetData()
    {
        DataTable table = new DataTable();

        table.Columns.Add("Student", typeof(string));
        table.Columns.Add("Score1", typeof(int));

        table.Rows.Add(new object[] { "0806014562", 40 });
        table.Rows.Add(new object[] { "0806014562", 50 });
        table.Rows.Add(new object[] { "0806014562", 70 });
        return table;
    }
Workarounds:
1) Use format string to add the desired missing zeros when parsed.

<LabelsAppearance DataFormatString="0{0}"></LabelsAppearance>

2) Add items programmatically

    protected void Page_Load(object sender, EventArgs e)
    {
        Radhtmlchart1.DataSource = GetData();
        Radhtmlchart1.DataBind();

        DataTable currDT = GetData();
        for (int i = 0; i < currDT.Rows.Count; i++)
        {
            AxisItem currItem = new AxisItem(currDT.Rows[i]["Student"].ToString());
            Radhtmlchart1.PlotArea.XAxis.Items.Add(currItem);
        }
    }