I think this is my problem with the song too but to be fair I think this is only a problem during the first half of the verse, once they introduce the piano it starts flowing smoothly together. It's also not a problem for me during the chorus because the layerd harmonisations and chanting create their own melody. But during the verses it truly sounds like they took the singing from one song and inserted it over the melody of another song.
It does get better after the first half. The roll it up ( I don't remember if those are the exact lyrics) part fits perfectly. I also liked the the bridge wasn't over the top. It was a nice touch and it fit as well.