show data label when the values are negative

I have a bar chart where I'm trying to get the data labels to show. When the values are all positive the data labels appear fine. When I mix in some negative values, the datalabels don't show:

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
           xmlns:s="library://ns.adobe.com/flex/spark" 
           xmlns:mx="library://ns.adobe.com/flex/mx" width="100%" height="100%"
           creationComplete="fillArray();"
           >

<fx:Script>
    <![CDATA[
        import flash.events.Event;

        import mx.collections.ArrayCollection;
        import mx.controls.Alert;

        public var array:Object=new Object();
        [Bindable]
        public var ac:ArrayCollection=new ArrayCollection([]);

        private function fillArray():void{

            array=new Object(); 
            ac=new ArrayCollection([]);

            for(var k:in开发者_如何学JAVAt=-12; k<10; k++){ //datalabels are visible if I start k at 0
            array=new Object();
            array['val']=k;
            array['label']=k;
            ac.addItem(array);
            }



        }


    ]]>
</fx:Script>

<mx:BarChart id="barChart" width="100%" dataProvider="{ac}">
    <mx:verticalAxis>
        <mx:CategoryAxis dataProvider="{ac}" categoryField="label"/>
    </mx:verticalAxis>
    <mx:series>
        <mx:BarSeries xField="val" labelPosition="outside"/>

    </mx:series>
</mx:BarChart>  

EDIT: Is this a bug in Flex and (therefore) unanswerable?

Seems to me that this is a problem of size, with 22 bars the label are too small to see, so they don't show. if you change the range of the "for" to:

for(var k:int=-5; k<5; k++)

you should be able to see all the labels of the chart.