Yes, in your version the bug is fixed (at least the one I know of).
But perhaps you've found a new bug? If you manage to reproduce the problem, let me know.
Also, it would be interesting to know how much time elapsed between the last bookings on these slots. In the Moodle logs, you can find an event every time that a student makes a booking (event scheduler\booking_added). Perhaps you can find the bookings of those students that last booked into the overfull slots. Are they minutes, seconds, or maybe milliseconds apart? (That would indicate whether it's a problem in the software, or maybe a synchronization problem in your particular setup.)