I find that mixed case conversion doesn't upper-case the starting letter if it is preceded by a symbol. For example, I frequently add "[Remix]" to the end of song titles. If I run a case conversion on "song title [remix] it will change to "Song Title [remix]".
I believe this also happens for hyphens and '. There may be other undesirable characters that are not being seen as non-word characters.
Example: $caps(%artist% - %album% - %track% - %title%)
This example converts the given string to normal case. The second parameter is optional and specifies additional characters that triggers upper case.
artist - ALBUM - 01 tItle converts to Artist - Album - 01 Title