Hi Jan,
Thank you for your patience. In the reference sample, the content scrolling (scrolls per item) is enabled by default in the "DataGrid.xaml". You can simply set this "CanContentScroll" value to false like this,
<Setter Property="ScrollViewer.CanContentScroll" Value="False"/>
Note: Currently we don't support Virtualization and Overlapping features together.
Thanks,
Raja.