Building on a shared wall

My neighbor is building a one story masonry rear yard extension. There is a shared party wall, about 2 ft tall, that separates our properties. (I’m not sure if shared wall is the proper terminology since it’s not full height)

In order to maximize space, they are vertically extending their half of the shared wall by laying a cement block wall on top of ‘their’ half. Is this proper construction practice? They have permits.