Hi!
So, yeah - the 180 video is actually hiding the other part of the dome otherwise the texture repeats. this was the acceptable solution when it was implemented. You can follow the thread here - 180-degree 3D video (VR180) support?
Since we project the video as material, it is applied to the entire dome. to make sure the texture is not repeated, we are setting the texture accordingly and hiding half of the dome with a black screen.
Want to share with me the video you are trying to use?