In the video you're only showing a weird rotation inside the prefab viewer, so I assume that's the problem? Ever since 2.0.3 or so, Dark Radiant's prefab (and model?) viewers changed from rotation around the origin of your pf/model to 3D viewport controls. You're not seeing the prefab rotating weird due to a wrong origin, that's on the camera. If you right click the viewer window, in fact, you can go into freelook mode just like the 3D viewport.
I think it was brought up once or twice in the DR release threads and I don't honestly know if it was intentional. Me, I don't really like it that much, since now some prefabs with bad origin points are invisible and impossible to spot in the viewer.
Edited by Spooks, 12 March 2017 - 02:21 PM.