Passer invenit sibi domum et turtur

The irregular modality of this Communio is normalized in this particular source by lowering its final to D instead of the original, likely pre-Octoechos E. The downward shift seems to happen on 'et (deus meus ...)' by opting to e-f-g instead of e-g-a and thus continuing down by a tone. See Graduale Novum, p. 82 for a recent rendition employing F# in order to preserve the final on E.