FieldDoesNotExist if remove foreign key and remove unique constraint at the same time

[Jindi Wu]

Remove foreign key b and unique_togetehr constraint from model like following:

class A(models.Model):
    name = models.CharField(max_length=10)
    b = models.ForeignKey('B')

    class Meta:
        unique_together = (('b','name'),)

class B(models.Model):
    text = models.CharField(max_length=10)

-->

class A(models.Model):
    name = models.CharField(max_length=10)

    class Meta:
        unique_together = (('name'),)

class B(models.Model):
    text = models.CharField(max_length=10)

Such error will be thrown.

raise FieldDoesNotExist('%s has no field named %r' % (self.object_name, field_name))
django.core.exceptions.FieldDoesNotExist: A has no field named 'b'

However if swap the order of generated two operations within the migration AlterUniqueTogether and RemoveField, it'll work.

Is this a bug or am I using Django the wrong way?