Case insensitivity doesn't work for Titles with Mixed Case (see [[WP:MIXEDCAPS]]).
We had a bot creating thousands upon thousands of redirects from the small-case versions of mixed-case articles. http://en.wikipedia.org/wiki/User:BOTijo
This is obviously sub-optimal to simply fixing the case-insensitivity in the search box to find the mixed case article automagically.
We've revoked the bot's authorization in hopes this bug can be fixed.