Wannabee,
Not questioning your experience, but something that took me years to figure out was that at times I had too much bag. I would fall asleep nice and warm and wake up freezing my butt off. The problem was I would sweat and then get chilled. I have several bags and try to match the bag to the trip I am taking. I have an arctic bag that has kept me comfortable in temps below -30. That bag is worthless for me in mild climates, even unzipped. Anyhow, you may have figured this out quicker than I as I'm probably not the sharpest knife in the drawer! For me the Treker has worked great for what it was designed for. I agree that a liner is a great way to keep the inside of a bag clean and add a little warmth, I just thought I'd give an alternative.
Norkal