Hi Christoph,
Thank you for your interest in Syncfusion products.
I could able to get the two bars in the same row with the code snippet you used. Also the position of bars gets changed when you incremented the values of RowIndex and RowOffset properties.
Could you please try to modify the below sample and reproduce the same.
http://websamples.syncfusion.com/samples/Tools.Windows/F62193/main.htmAlso kindly let me know the Essential studio version you are using now.
Regards,
Jaya