Maybe it has something to do with your receiver. Even though other DTS-ES tracks may work, this title may not.
I have a similar problem with my copy of the Haunting. It was the first ever DTS Discrete dvd and my HK 525 doesn't want to pick up the 6.1 flag and just decodes it in DTS-ES matrix instead of ES Discrete. Panning in the rear channels can sound odd sometimes. I have a copy of the DTS demo disc #4 and it has a (flagged) DTS matrix and plays (and sounds) a little smoother in the rear.
Any other dvd that ever had a DTS 6.1 Discrete track on them played fine. Odd huh?
Maybe you have a similar problem?