On Booking.com extranet the same room with Standard rate was closed for reservations as well.
However, you can see that there is still 1 availability for Double Room with a Non refundable rate. Myallocator manages only XML enabled rate plans, in this particular case, it is only Standard rate.
That is why availability wasn't closed for Non refundable rate, and the booking was allowed.
There are 2 ways of fixing it.
1. Manually manage availability for this rate plan on the Booking.com extranet.
2. Contact your Booking.com account manager and ask him/her to XML enable this rate plan. So both availability and rates are derived from the Standard rate and thus managed by Myallocator.