For the time being you can use the following workaround:
1) Either hide the chart with visibility:hidden instead of display:none
2) Or use the following workaround:
		<div id="div1" style="display: none;">
			<telerik:RadHtmlChart runat="server" ID="ColumnChart1" Width="600px" Height="400px">
				<PlotArea>
					<Series>
						<telerik:ColumnSeries Name="Product 1">
							<SeriesItems>
								<telerik:CategorySeriesItem Y="1" />
								<telerik:CategorySeriesItem Y="2" />
								<telerik:CategorySeriesItem Y="3" />
							</SeriesItems>
						</telerik:ColumnSeries>
					</Series>
				</PlotArea>
			</telerik:RadHtmlChart>
		</div>
		<input type="button" onclick="showChart(); return false;" value="Show Chart" />
		<script>
			Telerik.Web.UI.RadHtmlChart.prototype._getMainConfig = function () {
				var that = this;
				//when visible is false - nothing is sent from the server to save transferred data
				//e.g - there are properties set but visible is false - we do not need to send those properties amyway
				//that is why - set visible: false when nothing is sent from the server
				that._options = $telerik._getPropertiesParameter(that, that.constructor);
				that._cleanUpConfigProperties();

				that._options["theme"] = that.get_skin();
				//that._options["visible"] = $(that.get_element()).is(':visible');
				that._options["title"] = that._chartTitle ? that._parseObject(that._chartTitle) : { visible: false };
				that._options["legend"] = that._legend ? that._parseObject(that._legend) : { visible: false };

				if (that._chartArea) {
					that._options["chartArea"] = that._parseObject(that._chartArea);
				}

				if (that._isSparklineChart()) {
					that._setMinimumSparklineWidth();
				}

				if (that._plotArea) {
					that._configurePlotArea();
				}

				if (that._series) {
					/*jshint evil: true */
					that._options["series"] = eval(that._series);
					/*jshint evil: false */
				}

				if (that._isStockChart()) {
					that._configureStockChart();
				}
			}
		</script>