I done a small hack of source code, and it seems this is manager in file app/lib/BaseLookupController.php.
After adding the following line:
die('can_quickadd_'.$this->opo_item_instance->tableName());
This is returning the required permission can_quickadd_ca_list_items, but it seems this is missing from list of permissions.
I added then the following block in to app/conf/user_actions.conf
can_quickadd_ca_list_items = {
label = _("Quick add list"),
description = _("Allow user to quick add list")
},
Then the form return "Create?" when searching something missing, but this is not doing anything.
I guess something is definitely broken with this feature.