Hi, I took this test and everything was fine. Unfortunately, it seems like there are some faulty K550s out there... It is also possible that the first revisions of this headphone were all flawed, there is some anecdotal evidence that points to this conclusion so far (look at the varying measurement results, as well as the varying subjective evaluations). First revision K550s seem to suffer more from the shouty upper-mid issue that some people have been reporting. All of this could have been caused by the fact that the K550 is not built in Austria, like most other AKG headphones. None of this has been confirmed by AKG so please keep this in mind.
With all this said, I think you should have your headphones replaced. If the drivers are so imbalanced that you can actually hear the difference, it is certain that they will replace the headphone for you without any problems.