Oh i didnt even notice that, it happened in one of my playthroughs too i think its because you arent really travelling into the future the game uses the other portal as a way to teleport you to a place in the scene that is currently loaded however there are rules that the cube must follow in order to get into the future thus if all of them are checked the cube is permitted to go through the portal but there are also rules that make it stable in the present that must also meet all the requirements so i think that glitch happened couse the game bugged out sent a false check in the present and since you were already in the future and were holding the cube that now shouldn't even be there the game freaked out and did some weird stuff