Unlike the Orthodox, we've never held ourselves to be eternally bound by the disciplinary decrees of Councils, only by the doctrinal ones. And the question of whether or when one kneels is a matter of liturgical discipline, not dogma.
The custom (and the current law worldwide) in the Latin Rite for centuries has been to kneel at least for the consecration. American law requires kneeling throughout the anaphora. It's customary to return to the kneeling position after Communion.
" Unlike the Orthodox, we've never held ourselves to be eternally bound by the disciplinary decrees of Councils, only by the doctrinal ones. And the question of whether or when one kneels is a matter of liturgical discipline, not dogma."
Truth be told, C, the Greek Church takes essentially the same position, for which reason we get a good deal of flak from the Slavs. You know, there are other disciplinary canons which say we cannot go to a Jewish doctor or ride in a public conveyance with Jews, but nobody pays any attention to them either. As a general proposition, though, we are rather scrupulous about adhering to the disciplinary canons of ecumenical councils.
Rules for posture of the laity at Mass were always a matter of custom and not law until 40 years ago. This is why if you attend different TLMs, there may be slight differences when the people stand, kneel, and sit.