When you run a sentence : "The quick Cat jumped over the lazy CAT6"
through WhitespaceAnalyzer this is what it does to it:
[The] [quick] [Cat] [jumped] [over] [the] [lazy] [CAT6]
As you can see "Cat" is clearly with true case in the list, you should be able to find it. How are you querying it? During query what analyzer are you using?