Thank you for bringing this issue to our attention. It is indeed browser-specific (IE11), and is observable only when the scrollable part of the Grid is clicked before scrolling to a point where a new data request is made.
Unfortunately we are not sure what is causing the undesired behavior, and will need time to investigate the issue, and try to fix it. It is now logged as an issue in our GitHub repository, and you can follow it there:
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Telerik by Progress