receiver decoding 6.1 DVD's but not blu-rays - ugh!

[Dubstar]

essentially the problem I'm having is that my receiver (Yamaha RC-V665) is decoding 6.1 DTS and from DVD's:

Toy Story I/II
Bad Taste (DTS-ES)

(on the receiver the rear center channel is lit up indicating that the speaker is in use and sound is definately coming out from it)

but it's not decoding 6.1 audio from the following blurays:

Harry Potter and the Sorcerer's Stone (Ultimate)
Terminator 2 (Skynet Edition) (DTS-HD MA 6.1)
Star Wars Episode I: Phantom Menace (DVD)
Monsters Inc. -

it's decoding 5.1 but not indicating the rear center channel track is on and no sound is emitted

my bluray player is a LG BD390

Why it's decoding DVD's correctly, but not blurays makes no sense, is this a setting I might have ticked on my bluray player or is the problem on the receiver's end?