1. Create a basic Level Sequence and a Cine Camera Actor.
2. Set the Squeeze Factor to 2.0 in the Lens Settings of the Cine Camera Actor.
3. Assign the Level Editor Viewport to look through this camera, Examine what is visible in the Level Editor Viewport, after resizing the Level Editor Viewport to have a size that is approximately 1920x1080
4. Add this Level Sequence to MRQ, and set the Output Resolution to 1920x1080 (which is the default)
6. Compare the resulting images to what you see in the viewport
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-200538 in the post.