Ok so lately I have been wondering something about Korean names and the way they are romanized so if anyone has a legit explanation please say so.  

The name 찬열 (Chanyeol) is romanized 'properly' as I was taught in the korean course I took last year in school, but 백현 (baekhyun) is not.

here's my issue... they have the same korean vowel "ㅕ" but it is written Chanyeol and Baekhyun (where it 'technically' should be Baekhyeon)

IM REALLY CONFUSED PLEASE EXPLAIN THIS TO ME!