Jet Engine Question

Rating: 8/10 (14 March 2005)

I have read in many comments on this site that the whole idea of the movie is that Donnie has to send the artifact(the jet engine) back through the portal from the tangent world because having 2 identical artifacts in the tangent universe was making it unstable and going to cause the world to end. If so surely at the end of the movie when Donnie is in bed laughing in the real world and the engine comes through the roof and kills him there are now two identical artifacts(jet engines) in the real world now i.e. the one in his bedroom that came through the portal and the one on the plane somewhere else in the real world?? This makes no sense