Second-level nested InlinePanel child objects are not copied for translation

[gasman]

If a snippet model definition contains two nested levels of InlinePanel children, then copying an item for translation results in the grandchild objects being moved from the source record to the translated record, instead of being copied.

Starting with a fresh Wagtail 6.2a0 instance with wagtail-localize installed and configured as

WAGTAIL_I18N_ENABLED = True
WAGTAIL_CONTENT_LANGUAGES = LANGUAGES = [
    ("en", "English"),
    ("fr", "French"),
]

and home/models.py as follows:

from django.db import models

from modelcluster.fields import ParentalKey
from modelcluster.models import ClusterableModel
from wagtail.admin.panels import FieldPanel, InlinePanel
from wagtail.models import Page, TranslatableMixin
from wagtail.snippets.models import register_snippet

class HomePage(Page):
    pass

@register_snippet
class Event(TranslatableMixin, ClusterableModel):
    name = models.CharField(max_length=255)

    def __str__(self):
        return self.name

    panels = [
        FieldPanel('name'),
        InlinePanel('sessions', label="Sessions"),
    ]

class Session(TranslatableMixin, ClusterableModel):
    event = ParentalKey(Event, related_name='sessions')
    name = models.CharField(max_length=255)

    def __str__(self):
        return self.name

    panels = [
        FieldPanel('name'),
        InlinePanel('speakers', label="Speakers"),
    ]

class Speaker(TranslatableMixin, models.Model):
    session = ParentalKey(Session, related_name='speakers')
    name = models.CharField(max_length=255)

    def __str__(self):
        return self.name

    panels = [
        FieldPanel('name'),
    ]

• Add French as a locale
• Create an Event snippet with name = Christmas, session name = Christmas Day, speaker name = Santa Claus
• Check the database and note the ID of the created record in home_speaker
• From the snippet listing, select Translate -> French, enter translations ("Noël", "le jour de Noël", "Père Noël"), then "Publish in French"
• The original English event is now missing the record for Santa Claus
• Checking the database again shows that the original record in home_speaker has been updated with the translation and attached to the new Session record, instead of being copied.