First, let me explain how the timebar and chart are integrated, because I suppose you are using the built-in integration feature. Baically, the data that the chart shows is filtered, based on the selection in the timebar. As a result, in case you have only one datapoint for a series in the filtered data, it will show as a point and not as an area. And in case there are no datapoints for a series in the filtered data, you will not see this series.
Now, regarding the change in the ZIndex for the different series. Basically, the ZIndex order of the series in the chart, depends on the data for the series. That is why, at some point, filtering the data for the chart through the timebar might lead to different ZIndex order of the series.
In case the built-in integration of RadChart and RadTimeBar does not fit your requirements, you should be able to implement your own integration logic, using the features of the two controls.
the Telerik team
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