Clearing Document Date do not follow the define clearing date BKPF-BUDAT in F-03.
My user received the unpresented check statement from the bank on 31 Dec 2010. As 1 Jan 2011 is holiday and he came back to the office on 5 jan 2011. He post manual upload (Debit : Bank Outgoing and Credit : Unpresented Cheque) posting date 31.12.2010 (period 12/2010 and 01/2011 still open) . Hence the next step (same date on 5 Jan 2011) is to clear the Bank outgoing using F-03. He put 31.12.2010 as his Clearing date BKPF-BUDAT but when the system post the clearing date is 04/01/2011.