Aeterna Dei Sapientia §19

¹⁹ St. Leo's delay in ratifying the acts of this council is further proof of his genuine concern for the Church's unity and peace. We cannot attribute this delay to any remissness on his part, or to any cause of a doctrinal character. Obviously his intention—as he himself explains—was to thwart the twenty-eighth canon, which voiced the agreement of the Fathers of the council to the primacy of the See of Constantinople over all the churches of the East.