Plus, the colder the beer, the more it numbs your tastebuds.
As for the differences between the brews, it sounds like the ones where you're using darker roasted malts (Stout, Brown) exhibit the problem and the the ones that don't (Tripel) don't. It probably doesn't happen to a significant degree with a partial mash, but dark roasted malts can drive your mash pH too low and that can cause some off flavors. Maybe try measuring your partial mash pH and adding something like pickling lime to bring it up if it's too low.