Hello Franz,
Thank you for your interest in syncfusion products.
I am afraid that I am unable to reproduce the issue. I have tried several scenerio i could not see your reported issue in our samples. Please refer to the attached screen shot which illustrates the same.
Hope this will be helpful for your reference.
{Installed path}\Syncfusion\EssentialStudio\10.2.0.56\Windows\Grid.Grouping.Windows\Samples\2.0\Getting Started\Data Binding VS Demo\
Please let me know if I any misunderstood your reported issue.
Regards,
Ragamathullah B.
Video_51a4d9df.zip