I'm not sure what you mean. Selection in the Planner is indepdent from the items in positions.
Can you provide more details / step by step info on how to see the problem you experience?
I'm inserting items by code in planner.
This is not the default behavior.
I can only assume you had set Planner.PositionAutoSize = true that causes this behavior. If you do not want this, set Planner.PositionAutoSize = false.