Hello Saidarao,
The behaviour you described is the normal system design.
But if you want to use the planned activity in every case, you would have to apply a pilot release note 794150.
It is a small modification to solve your request. But since you cannot find it in portal directly, you would have to create a customer message to SAP and mention details of your problem, then the note would be then added and you would be able to implement it then.
Please create the customer message with component CO-OM-ACT-F.
Best regards,
Jason
