Looks like English is not the only language with inexplicable exceptions...hahaha
well yeah haha - it is a language and languages are, of course, living things -- anyway the pronunciation you learn from a native of Gwangju might get corrected by a person living in Busan (if they hear it coming from a foreigner) -- and vice-versa
a couple of interesting examples:
서산 (the city) --if you pronounce it as written almost nobody will understand you --I don't think the actual pronunciation can even be properly represented in Hangul it sounds something like 서-오 싼
-and-
해돋이 (sunrise) - which sounds like 해도지
so anyway I guess the best we can do is listen to and imitate native speakers as closely as possible