Duplicate reservations in Room Reservations DB

We’re getting ready to upgrade our room reservations DB from 4.6 to 6.3. In testing we’ve found that you can still duplicate reservations if 2 people create a reservation for the same room at the same time and submit at the same time. We thought that without the autoprocessing agent this was fixed and found some tech notes on how the router parses out the reservations. But haven’t found any mention of duplicates. Anyone having problems in production?