Hello, Thomas,

The provided sample project and video are greatly appreciated. I can reproduce the problem on high dpi scaling. I have logged this issue in our Feedback portal by making this thread public. You can track its progress, subscribe for status changes and add your comments on the following link - feedback item.

I have also updated your Telerik Points.

To work around this you can set the MinimumSize property or use the solution provided in the project if it is suitable for you:

 private void radMenuItem1_DropDownOpened(object sender, EventArgs e)
        {
            var item = (sender as RadMenuItem);
            item.DropDown.MinimumSize = new Size(0, 0);
        }

I hope this helps. Should you have other questions do not hesitate to contact us.

Regards,
Nadya
Progress Telerik