Quirks Mode(s) is about the only other suggestion. There is one aspect of using DOCTYPEs that is critically important for character encoding declarations. In Internet Explorer nothing must precede the DOCTYPE declaration in a file. If any character appears before it, the document will be served in quirks mode.
Albeit I could see "no difference". Thus it's either that 'browser version' or your configuration. I cannot really see how quirks modes would effect it to such a degree regarding rendering of fonts.
Although CJK rendering can have strange rules associated with it. In [URL="http://en.wikipedia.org/wiki/CJK"]CJK environments where there are several different multi-byte encodings in use, auto-detection is also often employed.