Why does steamed potatoes sometimes have a smooth, banana-like texture?
Could it be you are not using the same type of potatoes all the time? Different varieties of potatoes do have very different textures. The ones with the brown, rough, dusty skins ("russet" I think they are called?) usually cook up with the fluffy, dry, almost "sparkly" flesh. The smoother skinned ones tend to have denser, waxier texture inside. The pink, smooth ones ("rose" or "early rose") seem to fit the description of "looking dull" inside when cooked.