A poster in the Apple Forums recently asked why certain Simplified Chinese characters did not look exactly the way he expected them to, giving as examples bao1 (U+5305) and fang2 (U+623F). Looking these up in the Character Palette, I discovered that they are characters where the Chinese and Japanese versions are visibly different. You can compare them here. The first column is Japanese, while the second two columns are Chinese.
So it appears that the poster's apps were using OS X's Japanese fonts instead of the Chinese ones that he wanted. Aside from switching to the correct font, one possible solution for this is to go to System Preferences/International/Languages and make sure that Simplified Chinese (简体中文) is higher on the list than Japanese (日本語).
This issue arises as a result of the unification of the Han Script in Unicode, under which slightly different versions of characters were given the same code point. Fonts produced for specific languages will nonetheless retain the different versions. For more info you can check here.