Error when updating a dynamic association in a newly created object

This test also fails in master.

I created a PR for 6.0.x.BRINQA, but it might not be the best solution.

def "Test update newly created object"() {
setup:
def victor = new Pet(name: 'Victor')
def fritz = new Pet(name: 'Fritz')
def franz = new Pet(name: 'Franz')
def heinrich = new Pet(name: 'Heinrich')
victor.buddies = [fritz, franz]

when:
victor.save()
heinrich.save()
session.flush()

then:
victor.buddies.name.sort() == ['Franz', 'Fritz']

when: "Adding an element"
victor.buddies.add(heinrich)
def cousin = victor.cousin

then:
victor.buddies.name.sort() == ['Franz', 'Fritz', 'Heinrich']

when:
victor.markDirty("buddies")
victor.save()
session.flush()
victor.discard()
victor = Pet.findByName("Victor")

then:
victor.buddies.name.sort() == ['Franz', 'Fritz', 'Heinrich']
}

Start by reproducing the failure in the shown Groovy test, especially the dynamic buddy association and the save/flush sequence. Done means the test passes: adding Heinrich to victor.buddies survives save, reload, and the final association assertion.

Written by the indexing model from the issue text.