I just got the Abyss on DVD. On the package it says Dolby 5.1 surround. When I play it there is a 10 second intro for THX surround in which my receiver's display shows that it is decoding Dolby Digital and receiving the six channels. However, once the movie starts the display changes to Dolby ProLogic II and indicates only two channels of audio. All other DVDs seem to work fine. Is there a problem or are they being misleading; calling it 5.1 because there's an intro in digital mode?