drilldown label concatenating in clustered bar chart

Hi

I use PBI Desktop for Report Server (June 2017)

I have two exact same Clustered Bar Charts on a page (the second one is a copy of the first one)

On the second one, I changed the axis hierarchy.

First Chart:

• Axis hierarchy: Planner, PartTitle, Order
• Drilldown: Category labels are NOT concatenated. 
• 
•  We are on the second hierarchy level, only PartTitle is displayed.

Second Chart:

• Axis hierarchy: PartTitle, ComponentTitle, Order
• Drilldown: Category labels are CONCATENATED
• 
•  We are on the second hierarchy level, PartTitle AND ComponentTitle are displayed.

WHY?

I didn't find any property to control this behavior...

Greetings,

Roli