I think that I have figured out why people are at times slow to kneel after singing the Sanctus and slow to stand up after singing the Great Amen: because the music is different during Lent! It's amazingly frustrating that after all these Lenten Sundays for all these years, it still feels awkward. I guess Lent is supposed to disrupt our habits. We are supposed to stop and think and challenge our routine. And the Catholic liturgy is there to help by throwing off our rhythm where it matters most, in our worship of God.