With the post relationship field: when you add an object relationship, the object will disappear from the left-hand column and will be placed in the right-hand column.
This makes perfect sense to me. But, when the post is saved and the screen reloads the left-hand column is repopulated with all the objects again, including the objects that were selected (that is to say, the objects that were removed from the left-hand column).
The screenshot below shows the behaviour after the post is saved.
With the post relationship field: when you add an object relationship, the object will disappear from the left-hand column and will be placed in the right-hand column.
This makes perfect sense to me. But, when the post is saved and the screen reloads the left-hand column is repopulated with all the objects again, including the objects that were selected (that is to say, the objects that were removed from the left-hand column).
The screenshot below shows the behaviour after the post is saved.