i notice the same thing as you every time i work with my hd and it make me feel
i have notice other bad things :
1) when you read one track on ouput 1 (and have ten other tracks ,output :2,3,4,,,,,ect witch are muted ) solo the track one and unmute the others tracks : the sound isn't the same ;
2)solo the track one again,put a effect send on the track mute and unmute the send :is the sound the same ?!!!!
3) and more ......
thierry