Yes, when Dish Anywhere switches video quality, the screen goes black for a couple of seconds. It has been doing this for years now. I don't think that there is anything you can do about it, that is the way that Dish designed their software. If that really bothers you, you can try setting the video quality to something other than 'Auto'. I think that will prevent Dish Anywhere from changing the video resolution, so you will not get the black screen. However, you will also not get the benefit of the software automatically switching resolutions based on your download speeds.
If your internet is fast enough, you can set the video quality to HD, but if your connection slows down, you will get macro-blocking, stuttering, or no video, instead of a black screen for a couple of seconds.
BTW, Dish Anywhere questions have been posted here for a long time. This is the correct forum.