10 years ago
Perhaps the 'case sensitivity' could be related to the 'codepage' setting for your desktop's 'locale'. If you have multiple languages installed, your system's 'input method' could be sending UTF-N or UNICODE strings which the software manager would be handling differently than a single-character locale. Less likely but still a possibility is the 'input method' service you're using.
My setup is xim (default) with locale set to en_US.UTF-8 (>echo $LANG) and the search results in the Synaptic Package Manager and Software Manager are case-agnostic by default on a Linux Mint 14 (nadia) x686 (32 bit w/ 686 PAE kernel) desktop system.
The aptitude manual also specifically claims that the search feature uses case-insensitive regular expressions (http:///usr/share/docs/aptitude/html/index.html).
Perhaps others can post results for other input methods and/or locales to determine under what conditions (if any) searching in these programs becomes sensitive to character cases. Hopefully the OP can provide this information as well as their system's 'aptitude' config file(s).
Using your example, Gnome-Disk-Utility returns the same result as gnome-disk-utility in Mint 12, so I'll mark as implemented
New -> Implemented
Synaptic has had issues with me in the past too.