In Opus 12, I select a .mov video file shot in portrait mode (1920 x 1080) and open the viewer pane. The image is rotated 270 degrees. Opening the video in VLC displays it properly. I've played with the setting for "Use EXIF information..." to no avail.
This Exif tag only applies to images. For videos it's a different one and Windows Media Player ignores it. If you want the pane to be correct, you need to transcode the video. But that's probably not worth the effort.