How can RFCUSER change purchase quantity of an STO?

[Former Member]

We have a case where STOs from a particular source are getting their original quantity changed by RFCUSER. This happens as follow:

1. A cross-company STO is created in APO.
2. The STO reaches ECC. It is shown as created by RFC.
3. The mentioned quantity is issued by the warehouse.
4. Now, few days later, RFCUSER adds a schedule line in STO and this changes the purchase order quantity.This quantity is not yet issued by warehouse.
5. The new quantity added is not desirable. So, user tries to change it back. But, she's not able to do it as the new schedule line is grayed out and older schedule line quantity is issued.

Note: The changes made by RFCUSER can be seen in ME22. Normally, changes are made in ME22N.

Now I have two questions:

1. How RFCUSER added a new schedule line in the STO? As per my knowledge, STO is a confirmed receipt and APO system doesn't allow changes to a confirmed receipt.

2. Why system is not allowing change in schedule line quantity when the goods are not issued yet?