Co06 transaction

I am trying to re-allocate and de-allocate stock in this transaction.

Example

in stock 10 pc

Order 1 - created for 10 PC - confirmed schedule line date 21.03 ( pick pack time = 2 days and material is available 18.03)

Order 2 - created for 17 PC ( I get later date confirmation as per the replenishment lead time and pick pack time calculation, say 01.04.2016)

Now if I de-allocate the stock from Order 1

and try to run availability check on order 2- I expect - system will come back with earlier date for 10 pc( 18.03)

but  system says ATP quantity is zero..

Can you please help?

Thanks!

RT