Shifting of Schedule Lines

Here goes the scenario:

1. In the production environment, a Standard Order is created with Requested Delivery Date as 15th July 2014.

2. After all the data is entered, the system automatically shifts the Schedule Line Date to 21st July 2014.

3. If I create the same order in Quality/Testing Environment(Replica of Production Server), the schedule line confirm to 15th July 2014 only.

4. Enough Stock of material is available in both the environments and Material Master is exactly the same in both the environments.

Please let me know all the possible reasons that might be causing the shifting of Schedule lines in the Production Server.