Describe the bug
In WordPress Core, the wp_capabilities field uses the wpdb prefix, but we do not. There's code in Core that runs, for example, like $this->cap_key = $wpdb->get_blog_prefix( $this->site_id ) . 'capabilities';.

To Reproduce
Steps to reproduce the behavior:

1. Install WordPress with a custom prefix.
2. Try to map the capabilities field

Expected behavior
It should work the same as wp_capabilities, but it doesn't.