hbox + splitter + zkcharts, resizing fails

Steps to Reproduce

run the attached splitter-chart.zul

drag the different splitters (2nd row using the charts with red border)
resize the browser

Current Result

when using charts resizing using the splitter has no effect
browser resizing only works partially when increasing the browser width

Expected Result

resizing the splitters should work as with normal divs (1st row - green borders)

Debug Information

Workaround 1

the 3rd row contains a partial workaround for charts (css + extra helper div), to restore dragging the splitters - browser resizing still results in incorrect sizes

workaround 2

<splitlayout orient="horizontal" height="100%">
    <splitlayout hflex="2" orient="horizontal" height="100%">
    <div hflex="1">
        <charts hflex="1" type="pie" title="Browser market shares at a specific website, 2010"/>
    </div>
    <div hflex="1">
        <charts hflex="1" type="pie" title="Browser market shares at a specific website, 2010"/>    </div>
    </splitlayout>
    <div hflex="1">
        <charts hflex="1" type="pie" title="Browser market shares at a specific website, 2010"/>    </div>
</splitlayout>