I. They have possibly been misled by a wrong translation of his letter on the Incarnation to Flavian.
Leo, the bishop, to the whole body of monks settled throughout Palestine.
The anxious care, which I owe to the whole Church and to all its sons, has ascertained from many sources that some offense has been given to your minds, beloved, through my interpreters, who being either ignorant, as it appears, or malicious, have made you take some of my statements in a different sense to what I meant, not being capable of turning the Latin into Greek with proper accuracy, although in the explanation of subtle and difficult matters, one who undertakes to discuss them can scarcely satisfy himself even in his own tongue. And yet this has so far been of advantage to me, that by your disapproving of what the Catholic Faith rejects, we know you are greater friends to the true than to the false: and that you quite properly refuse to believe what I myself also abhor, in accordance with ancient doctrine. For although my letter addressed to bishop Flavian, of holy memory, is of itself sufficiently explicit, and stands in no need either of correction or explanation, yet other of my writings harmonize with that letter, and in them my position will be found similarly set forth. For necessity was laid upon me to argue against the heretics who have thrown many of Christ's peoples into confusion, both before our most merciful princes and the holy synodal Council, and the church of Constantinople, and thus I have laid down what we ought to think and feel on the Incarnation of the Word according to the teaching of the Gospel and Apostles, and in nothing have I departed from the creed of the holy Fathers: because the Faith is one, true, unique, Catholic, and to it nothing can be added, nothing taken away: though Nestorius first, and now Eutyches, have endeavoured to assail it from an opposite standpoint, but with similar disloyalty, and have tried to impose on the Church of God two contradictory heresies, which has led to their both being deservedly condemned by the disciples of the Truth; because the false view which they both held in different ways was exceedingly mad and sacrilegious.
Source: Letters (New Advent)