Physical Inventory Freezed but Can Still Invoice

Hi, guys.

Our user is doing physical inventory count in ECC 6.0 and the stocks are supposed to be freezed. But user noticed that warehouse can still do invoicing, thereby creating a physical inventory difference.

My questions are: (1) how to correct the difference, (2) what caused the other user to invoice the parts that are freezed during physical inventory count?

Thanks for your time.

Regards,

Rey