Doctrine optional OneToOne entity deletion - php

Question

I have two entities, a Flight and a Booking.
They are configured in a bi-directional one-to-one relationship, with the Flight underlying table holding the foreign key to the Booking underlying table.
The idea is that a Flight instance must be linked to a Booking, but a Booking can exist without a Flight.
/**
* #ORM\Entity
*/
class Flight{
/**
* #ORM\OneToOne(targetEntity="Booking", inversedBy="flight")
* #ORM\JoinColumn(name="bookingID", referencedColumnName="ID", nullable=false)
*/
private Booking $booking;
/// Rest of code removed for readability
}
/**
* #ORM\Entity
*/
class Booking{
/**
* #ORM\OneToOne(targetEntity="Flight", mappedBy="booking")
*/
private ?Flight $flight;
/// Rest of code removed for readability
}
I do not want to use cascading operations since a Flight can be removed without the Booking being removed (this is an extension of the idea stated above).
An issue arises when I try to delete both the Flight and the Booking.
Picture the following code:
// $flight holds a reference to $booking, as per the code above
$em->remove($flight);
$em->remove($booking);
$em->flush();
It would result in the following queries (logged by Doctrine)
START TRANSACTION
DELETE FROM flights WHERE ID = ?
INSERT INTO flights (redacted) VALUES (redacted)
DELETE FROM bookings WHERE ID = ?
ROLLBACK
Which I simply cannot understand.
If I remove the Booking directly through the underlying PDO Handle, it works perfectly, which means that is has to be a mapping issue, but I cannot see where I did something wrong. It's been driving me crazy for hours.