IE7: Imagemap Tooltip Not displaying

<?page title="new page title" contentType="text/html;charset=UTF-8"?>
<zk>
<window title="new page title" border="normal">
<imagemap id="myimage">
  <attribute name="onClick"><![CDATA[
    if (event.getArea() != null) {
      alert(self.getFellow(event.getArea()).getTooltiptext());
    }
  ]]></attribute><zscript>
import org.jfree.data.general.DefaultPieDataset;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PiePlot3D;
import org.jfree.chart.ChartFactory;
import java.awt.image.BufferedImage;
import org.jfree.chart.encoders.ImageFormat;
import org.jfree.chart.encoders.EncoderUtil;
import org.zkoss.image.AImage;
import org.jfree.chart.entity.PieSectionEntity;
import org.jfree.chart.entity.ChartEntity;
import org.jfree.chart.ChartRenderingInfo;


DefaultPieDataset pieDataset = new DefaultPieDataset();
pieDataset.setValue("C/C++", new Double(17.5));
pieDataset.setValue("PHP", new Double(32.5));
pieDataset.setValue("Java", new Double(43.2));
pieDataset.setValue("Visual Basic", new Double(10));

JFreeChart chart = ChartFactory.createPieChart3D("Sample Pie Chart 3D", pieDataset,true,true,true);
PiePlot3D plot = (PiePlot3D) chart.getPlot();
plot.setForegroundAlpha(0.5f);
ChartRenderingInfo info = new ChartRenderingInfo();
BufferedImage bi = chart.createBufferedImage(500, 300, BufferedImage.TRANSLUCENT, info);
for(Iterator it=info.getEntityCollection().getEntities().iterator();it.hasNext();) {
  ChartEntity ce = ( ChartEntity ) it.next();
  if (ce instanceof PieSectionEntity) {
    Area area = new Area();
    area.setParent(myimage);
    area.setCoords(ce.getShapeCoords());
    area.setShape(ce.getShapeType());
    area.setId(myimage.getId()+'_'+((PieSectionEntity)ce).getSectionIndex());
    area.setTooltiptext(ce.getSectionKey().toString());
  }
}
byte[] bytes = EncoderUtil.encode(bi, ImageFormat.PNG, true);
 
AImage image = new AImage("Pie Chart", bytes);
myimage.setContent(image);
</zscript></imagemap>
</window>
</zk>