I see this bug too, on v1.7 - probably related to the new boss floor. On some plays when I first enter the boss area, it moves+traps the player into the wall on the left like in the video. On other plays (or if I die and return to the boss area a second time), the floor fills in correctly, but the screen won't scroll to the right.
I haven't been able to tell what triggers the different behavior. Perhaps the place or direction when I jump up into the boss area?