Looks like they added the DOG for the encoding of the video file for iPlayer, not during the production of the 3D video. I think the DOG is always added at the end of the process (when producing the video file for use on iPlayer) as BBC ONE and TWO broadcast don't have DOGs so clearly it's not added in during production.
Unfortunately, they have failed to realise that adding it in at the end of the process isn't going to work for 3D videos. They should either modify their end-of-process iPlayer output for 3D videos or add it in during production (the latter probably is not going to work seeing as they will use this for generating various file formats for various outputs).
So it's simply a procedural error.