Do not call axis formatter for ordinate values.

apachedex/apachedex.js

-function formatValue(axis, value) {
-  var result = "";
-  if (axis.options.axisLabel) {
-    result = axis.options.axisLabel + " : ";
-  }
-  return result + axis.tickFormatter(value, axis);
-}
 function updateGraphTooltip(event, pos, item, previousIndex, tooltip, plot) {
   if (item) {
     if (previousIndex != item.dataIndex) {
       previousIndex = item.dataIndex;
       var plot_offset = plot.getPlotOffset();
       var offset = plot.offset();
-      tooltip.find(".x").html(formatValue(
-        item.series.xaxis, item.datapoint[0]));
-      tooltip.find(".y").html(formatValue(
-        item.series.yaxis, item.datapoint[1]));
+      tooltip.find(".x").html(item.series.xaxis.tickFormatter(
+        item.datapoint[0], item.series.xaxis));
+      tooltip.find(".y").html(item.series.yaxis.options.axisLabel + " : " +
+        item.datapoint[1]);
       tooltip.css("left", item.pageX - offset.left + plot_offset.left + 5
         + "px");
       tooltip.show();