Was about to write a huge mail with lots of code, but when trying to prove the problem, the Terms suddenly showed "false" and "true", instead of "False" and "True".
Some more testing showed that this depends on if the field is set as analyzed or not. Analyzed -> lower-case, Not Analyzed -> upper case
But IMHO boolean fields should be indexed unanalyzed, as i do not want to find things with "t" or tr"... But I might be wrong.
Still want the code?
_
Lars