We've tried to reproduce this issue, but everything seems to work as expected at our side.
I've prepared a sample project using our Telerik UI for WPF version 2015.3.1104 and a VirtualizingStackPanel with VirtualizingPanel.ScrollUnit="Pixel" as ItemsPanel for a RadListBox.
You can find the project attached as well as a video showing how it behaves at our side.
Could you please take a look and let us know if we are missing something?
Regards,
Polya
Telerik
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