Continuity mistake: When Lou and Nick are playing pool in the bar, Lou goes to break the rack and misses. When Nick goes to break them, the balls are racked in a different pattern. (00:50:10)
Continuity mistake: When the guys reach the end of their downhill run, they encounter Blain, who is irked by their "shenanigans," going so far as to shove Jacob to the ground. When he pushes Jacob the large two-way radio that is in his pocket falls and hits the ground in front of him. However, when the camera angle changes to show only Blain and Chaz, the radio is back in his pocket without him ever having to recover it from the ground.
Continuity mistake: When the guys are at the lodge in their room, and they're sitting around the table talking about the past, the glasses on the table keep moving around in each shot.
Continuity mistake: When the guys reach the end of their downhill run, the sun changes between shots.
Continuity mistake: When Adam eats the mushrooms in the room and speaks with Jacob, when he leaves Adam is wearing just the sunglasses, but in the next shot is also wearing a hat.
Continuity mistake: When the movie starts, Nick has his left hand over the bulldog's back and the right around the leash. When the phone rings, his left hand is now holding the leash, and the right one is grabbing the cell phone. The transition between both movements is missing.
Continuity mistake: When Phil throws the bags out of the trolley, the amount of bags changes drastically between frames.
Answer: It's just the rule they used for the movie; not a lot of thought was put into the time-traveling rules with the obvious inconsistencies the movie has throughout regarding it, especially in the ending.
lionhead