I have included a blank project showing the problem. When you move UMG widgets that have Text with Shadow Offsets applied, you get a constant resizing of the shadowing. This produces a flickering effect that really bothers your eyes.
Let me know if you need any more information, but its very reproducible.
I was able to reproduce this issue on our end. I have written up a report ( UE-21231) and I have submitted it to the developers for further consideration. I will provide updates with any pertinent information as it becomes available. Thank you for your time and information.