Facebook has recently changed its video behavior. When you click on a playing video, the video is taken to fullscreen.
On the fullscreen mode related videos are also shown so, I think the intention behind this behavior change is to increase the number of videos played in facebook.
But, this breaks the usability heuristics of Consistency and standards. The Expected/standard behavior is video should pause. This behavior is only for the facebook video player, rest of players(youtube,vimeo) which is inside the feed follow the standard behavior. Now the user has to keep in mind of the 2 different behaviors!
Did Facebook intentionally do this?