Multiple Bookings on the same hour not allowed

When selecting an item and making a booking for say 8-9:00 for “Item A” 2
Where “Item A” has 20 of them available.
Then selecting another item and trying to make a booking for 8-9:00 for “Item B” 3
It is not possible to select 8-9:00 for “Item B”

The outcome for a booking is I want:

Item A 8-9:00 2 Qty
Item B 8-9:00 3 Qty