From the player's perspective, it's not 3D. Just a bizarre 1920x540 video file. One makes it 3D by telling the TV that it's receiving 3D-SBS video; it's a manual process.
I forgot about that setting, Bill. Thank you for reminding me, I'll try it when I get home. I wonder if I could get around that by tweaking the mkv metadata and specifying an aspect ratio of 16:9. The Oppo BDP-93 respects that, right? Any ideas with which software I could do that, and also since not all the videos are in the mkv container, something easy for re-containerizing video? I realize this is getting off-topic, so I'll stop there.