Hi Matthias,
Thanks for your update.
We are sorry for inconvenience caused. We are unable to reproduce the issue. We have modified the sample based on the information provided by you in the last update.The sample can be downloaded from the following link.
http://www.syncfusion.com/downloads/Support/DirectTrac/95875/F10412-1965015907.zip
Screenshot:
Could you please try the above sample and get back to us whether you are able to reproduce the issue? If not, could you please give more information or by reproducing the issue in the above sample so that we could sort out the issue and provide you with solution. The information provided would be of great help in resolving the issue.
Please let us know if any concerns.
Regards,
Siva