I'm just wondering if that's the only part of the song(s) where he uses the backing track, or if any of those high notes before or in the chorus (in LOAP) are from that backing track, as well?

Could explain why he sounds so weird on the lower parts and then good on the higher parts. Maybe one could even trigger that based on the melody line, if the backing track is tempo-synched (or they're playing to a click track)? Like if the melody goes higher than X, then turn up the backing track, otherwise turn it down. Just a thought...