"Undefined expected int" exception when using SVG in a custom DataGrid cell

I want to include an SVG in a cell of a datagrid table.  I created a test class which shows a blue square.  The square displays just fine but when I click on it an exception shows up in eclipse (see below).   If I change the <svg> to be a string, a span or an img, clicking on that works without error.  Could someone tell me what am i doing wrong?   In the debugger the target of the click event shows as [object SVGRectElement] whereas when I flip the comments to, say, show an image instead of svg, the target is '<img src='foo.png'>.

-----
    private class CustomCell extends AbstractCell<String> {
        @Override
        public void render(Cell.Context context, String value, SafeHtmlBuilder sb) {
            if (value == null) return;
//            sb.append(SafeHtmlUtils.fromTrustedString(value.toString()));
           
//            sb.append(SafeHtmlUtils.fromTrustedString("<span>"));
//            sb.appendEscaped(value);
//            sb.append(SafeHtmlUtils.fromTrustedString("</span>"));

//            sb.append(SafeHtmlUtils.fromTrustedString("<img src=\"foo.png\"/>"));

            sb.append(SafeHtmlUtils.fromTrustedString("<svg><rect height='8px' width='8px' fill='blue'/>"));
        }
    }
-----



21:40:45.436 [ERROR] [... Uncaught exception escaped

com.google.gwt.dev.shell.HostedModeException: Something other than an int was returned from JSNI method '@com.google.gwt.dom.client.DOMImpl::getTabIndex(Lcom/google/gwt/dom/client/Element;)': JS value of type undefined, expected int
    at com.google.gwt.dev.shell.JsValueGlue.getIntRange(JsValueGlue.java:266)
    at com.google.gwt.dev.shell.JsValueGlue.get(JsValueGlue.java:144)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeInt(ModuleSpace.java:262)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeInt(JavaScriptHost.java:75)
    at com.google.gwt.dom.client.DOMImpl.getTabIndex(DOMImpl.java)
    at com.google.gwt.dom.client.Element$.getTabIndex$(Element.java:474)
    at com.google.gwt.user.cellview.client.CellBasedWidgetImpl.isFocusable(CellBasedWidgetImpl.java:74)
    at com.google.gwt.user.cellview.client.AbstractHasData.onBrowserEvent(AbstractHasData.java:731)
    at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1467)
    at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1406)
    at com.google.gwt.user.client.impl.DOMImplStandard.dispatchEvent(DOMImplStandard.java:256)
    at sun.reflect.GeneratedMethodAccessor54.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:55)
    at java.lang.reflect.Method.invoke(Method.java:613)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:338)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:576)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:284)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:324)
    at sun.reflect.GeneratedMethodAccessor52.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:55)
    at java.lang.reflect.Method.invoke(Method.java:613)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
    at java.lang.Thread.run(Thread.java:780)

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