When changing the zerolevel of a bar series, it seems to be that the zero level is substracted from the data values. For examples, if the bar y values are 20, 30, 40, and the zero level is 10, the bars are drawn from 0 to 10, 20 and 30, respectively, instead of from 10 to 20, 30 and 40, respectively. Is this a misunderstanding on my side, or is it a bug?