Still not fixed in the recent updates. Other video apps have a Display button to change the aspect ratio during video playback (toggling through Auto, Letterbox, Zoom, Stretch, and Native). The YouTube app is stuck on Zoom (or it's set to Auto and not working correctly). All they need to do is add that Display button to the playback menu and/or change the default aspect ratio back to Native. It's an easy fix if we can just bring it to someone's attention. Google employees don't seem to read these forums very often though.