consignment stock

Friends,

I have a doubt about Consignment processing. It might be simple question for you.

Intially i created consignment Fill up for 10 items

then customer stock became 10

created consignment Issues for 5 items

then customer stock became 5

Created consignment Return for 2 items

customer stock became 7

Finally when created Consignment Pick up for same 2 item

Customer stock became again 5 Why?

Another thing, if we collect material from customer premises in CR itself then why consignment pick up?

Please explain. I would like to give point for explanation.

Thanks