squashmigrations tries to alter M2M's through table

[Kevin Turner]

squashmigrations produced this pair of operations:

        migrations.AddField(
            model_name='tagcategorizeditem',
            name='tags',
            field=models.ManyToManyField(to=b'paks.Tag'),
        ),
        migrations.AlterField(
            model_name='tagcategorizeditem',
            name='tags',
            field=models.ManyToManyField(to=b'paks.Tag', through='paks.ItemTag'),
        )

which fails to execute because "you cannot add through= on M2M fields"

[Tim Graham]

It's helpful if you include the steps to reproduce the issue, otherwise it's a bit difficult to triage the ticket and check if the issue is fixed in a newer version of Django. Thanks!