ZoomCharts offers you drill-down with a simple touch. If you touch a bar/column/line, you can drill down into the next level. If you simply want to select it to get info, please long-press or right click the bar. This is the default behaviour which let you drill down in particular category. Can you please confirm if you can use this technique to navigate the charts?
If you need to view the "second" level for all "first" level categories, I would suggest removing the first level grouping from the settings at this time.