Because the tag editor only shows it.
Most tag editors will auto fix those badly formatted tag areas.
Good to know you can try a few editors but I hear you. For me I rarely edit tags but when I do, it's with iTunes. Some folk bristle at that software but I can't tell why. Maybe it's Apple, maybe they had an issue but here it is flawless.
My specific recommendation is to check download.com and try the top five folk like. Just like iTunes you may hate what I choose.