During one of the action scenes at Ken's house you can clearly see that the sparks that are supposed to show the effects of bullets hitting a wall, are actually coming out of a pipe attached to the wall.
When machine guns are fired during slow motion shots, the sound effects aren't slowed down.
When Kit gets shot in the basement, we can see a shadow of the camera.
Reflected in Mark's glasses throughout most of the final battle.
Nobody ever told Lung that his daughter is dead. Yet even Ken acts like it's a given without being told by anybody from Hong Kong.