we have a automatic cancellation program
I presume, it is a billing document cancellation program and your issue is when you tried to cancel a billing document dated 30th Jun'14, the accounting document was posted on 1st July'14. Let me know if my understanding is correct.
For information, in normal circumstances, the field BUDAT in BKPF is copied from VBRK-FKDAT which is hard coded and I am not sure, in your case, it is not happening.
G. Lakshmipathi