As the title says, the root component transform doesn’t change if you first translate and rotate a component under the default root component and then make that translated and rotated component the new root. See pictures:
I was able to reproduce this issue in a clean project. I have written up a report ( UE-21010) 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.