By default, all the custom URIs are sanitized and lower-cased (just like the slugs are filtered with native sanitize_title_with_dashes() function).

For example, products/LEATHER-JACKET is automatically converted (when the custom URI is saved) to products/leather-jacket.

Since 2.0.5.5 version, you can disable strtolower() function and stop lower-casing the custom URIs. All you need to do is to paste this line of code to your theme’s functions.php file:

add_filter('permalink-manager-force-lowercase-uris', '__return_false');