While it could be some dialect differences, i would imagine that seoul dialect is the one most people would be learning, and 우 and 오 would be clear in that case. If its from a song, maybe the lyrics are too fast and it just sounds similar from another word? I'm curious what song it is and where it sounds like that now, i'd like to listen to that part. Still, in your original question, 보다 should never sound like 부다.... at least based on my 12 years of listening to korean music and watching their drama. Hopefully a native speaker responds also.