Prior to v6.2, the default was to not convert to lowercase when indexing item text, and items indexed before then would have the original casing. Starting in v6.2, the default is now to lowercase to support case-insensitive search of non-ASCII content, and items indexed since then would be converted to lowercase.
If you only deal with ASCII text, you can turn this off to get the old behavior (see
https://www.kinook.com/Forum/showthread.php?t=5757), but you will need to re-index existing items that were indexed with the lowercase option enabled (re-import, sync, or change the item text).