Cannot change booked student

Cannot change the student in a slot after booking.

1. A slot is booked
2. When logged in as admin or as the teacher of the slot, on the slot edit page the student name is greyed and impossible to change

• The student can still cancel the booking
• The only way to change the booked student is by revoking the student on the main page and then editing the slot
• It's a site wide issue