Darn it!
I can't consistently replicate it. But just now I was watching a standard-def movie channel and processing PL II Movie. I flipped to a high-def channel and the LFE indicator illuminated. I hit Dolby Modes to check what the surround setting was on and it was PL II Movie. I then hit Dolby Modes once again and it properly switched to "Dolby Digital". I don't understand why it didn't originally default to Dolby Digital.
If I flipped back to the original standard-def channel and then back again to the high-def channel, everything defaulted properly. Shoot.
I'll keep trying