EDIT: The library content type that shows a problem is Mixed Content. I actually don't have any libraries in use that are Movies. I do have several TV Shows type libraries, and these display with correct aspect ratios. I checked multiple Mixed Content libraries; they are all stretchy.
The Emby server version is now updated to 220.127.116.11 this evening, and the Roku app was I believe 18.104.22.168 (or was it 3.0.84?) that showed before everything finished setting up when I went in and connected.
I'm attaching a log, starting I believe with when Emby started up after the update, and going through me playing around with the Roku just now. Note I had an aborted attempt to play Pirates of the Caribbean... it hung on the first attempt. Second attempt started fine. Not sure what that was about.
Again, stretchy icons I can live with; it's just a cosmetic thing, now duly reported.