refresh_from_db does not reset old values

[sjamaan]

I would expect foo.refresh_from_db() to exhibit exactly the same behaviour as foo = Foo.objects.get(pk=foo.pk), but foo.get_old_value('blabla') returns the original old value. Here's a sample from a test in an actual project where I wanted to test a validation check is only run when the type or status field changes.

		activity = activity_model(
			type='other', status='finished', finished_datetime='2017-10-14T13:00:00Z',
			start_km=0, end_km=0, start_fuel_level=0, end_fuel_level=0,
			assignment=assignment, allocation=allocation,
		)

		# Hack around a validation which triggers only if type changes by doing a bulk db query to change the type
		Activity.objects.filter(id=activity.id).update(type='load')

		activity.refresh_from_db()
		activity.get_old_value('status') # This returns "other", I would expect "load"

		activity = Activity.objects.get(id=activity.id)
		activity.get_old_value('status') # This returns "load", as expected