Why are public rates still visible in the booking engine when using a voucher code?

Even after applying a voucher code, the Mews Booking Engine still offers the other public rates. This is set up so the guests are offered other options even though the voucher grants them access to better rates. 

The Mews Booking Engine displays the cheapest rate as the option for booking and the crossed-out price for the most expensive rate in the same Rate Group, considering only the rates that are not restricted.