Very good, not perfect

The file locking feature is giving me headaches.
I want to lock only .pdf files, but the plugin locks all jpegs as well, resulting in a page with no images, backgrounds, etc… for non-logged in users.
I found this in UamConfig class:

'locked_file_types' => 'zip,rar,tar,gz',
'not_locked_file_types' => 'gif,jpg,jpeg,png',

but it doesn’t seem to do anything at all.