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 188.8.131.52 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: