Why is Django Postgres JSONField decoded differently depending on whether object is created or updated

I have a model with a PostGRES JSONField:

from django.contrib.postgres.fields import JSONField
# ... other imports ...

class Feature(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    # ... other fields ...
    meta = JSONField(default=dict)

And an importer command that either creates or updates features:

    my_meta = {
        'mykey': 'something',
    }
    feature = Feature.objects.filter(id=id).first()
    if feature is None:
        # The feature was not imported previously
        feature = Feature.objects.create(
            id=id,
            meta=my_meta,
        )
        print('CREATED FEATURE.META', feature.meta, feature.meta.__class__.__name__)
    else:
        # The feature was already imported above - update the existing feature with new metadata
        feature.meta = my_meta,
        feature.save()
        print('UPDATED FEATURE.META', feature.meta, feature.meta.__class__.__name__)

When running two different test cases, each creating one feature but testing the two branches of that 'if' statement, I get:

CREATED FEATURE.META {'mykey': 'something'} dict

UPDATED FEATURE.META ({'mykey': 'something'},) tuple

THE QUESTION

Why on earth is it decoding inside a tuple in that latter case?

NOTES

• Yes, my default is a callable (common issue ppl have with JSONField)

• No, I don't have django-jsonfield installed (which can cause weird incompatibilities with the native JSONField)