Hincmar of Reims in his Annals includes a letter of Pope Adrian II which makes the claim Anastasius the Librarian stole many important documents from Rome and seemingly attempted to doctor them. Whether the minutes of Nicea II were doctored before or after is something I am still studying (I presently am edging towards before), but it is a curious historical detail:

It is known to all the church of God what Anastasius did during the time of our predecessors as pontiffs, but also in what way Leo and Benedict, the excellent prelates, acted concerning him, is open to all. One of whom deposed him, excommunicated him and anathematized him, while the other stripped him of his priestly garments, among the laity he received in communion. Our predecessor, therefore, the most holy Pope Nicholas, afterwards, if he [Anastasius] had proceeded faithfully towards the holy Roman Church, would have received him in the bosom of the Church in the same way; but his unbelief now appeared to such an extent, that after the plundering of our patriarch and the removal of the synodal writings, which he had found decreed both on himself and on others of this kind by the most holy prelates at different times, he has made it so that the venerable synod’s decrees, which had been established by these holy pontiffs and confirmed under the threat of anathema, have been violated [violari] and stolen from us. Moreover, he has compelled men to sneak through the walls of this city like thieves, sowing discord between the most pious princes and the Church of God, and has sent a certain Adalgrim to the church. (PL 125:1241)

The preceding passage seems not to be about the minutes of Ecumenical Councils, but specifically local Roman councils pertaining to Anastasius’ ecclesiastical discipline and related Papal Decretals (perhaps the Pseudo-Isidorian Decretals themselves). The obvious implication was he absconded with them so as to alter the historical record, and the “canonical” consequences, for himself. The term “violated” in fact explicitly makes this rise above an implication.

A much more discerning eye must be used when reading Anastasius’ works as his own contemporaries, in fact allies (as Pope Adrian II reconciled two years later), accused him of attempting forgeries.