ATP check overwriting the manual dates

Hi Gurus,

We have activated ATP check at Schedule line category and Requirement level.

Issue - I create the order and system does the ATP check and looks at the available planning and suggests a particular date(example 02/01/2008) and i decide not to stick to that date for other reasons and extend the date(03/01/2008) out further and set a delivery block on the schedule line. also i check the Fixed date and quantity box and save the order.

When i come back to the order and remove the delivery block on the schedule line system automatically triggers the ATP and put the date back to 02/01/2007 .

Could any one please give an advice how to stop ATP trigger when delivery block on the schedule line removed?

Thank you

Srinivas Paturu