Over-booked rooms

Hi guys
i am facing some problems with number of rooms to sells. We only have two different rooms (one of each, as shown in attachement). In calendar I see there is correctly set "Rooms to sell", Room 1 has "one" and room 2 has "one". Somehow multiple reservations can be done on room 1 on the same date. Please see attachement, where one room is sold-out while other can still be booked even if there is only 1 available and that one is already booked. Looks like some bug, or there is some issue with my settings. Last year worked just fine.... Please help :)