This little quirk has to do with GP allowing you to use the same Single Use (as opposed to Recurring ) Batch ID multiple times. If GP stored the Batch ID (BACHNMBR) in the Open or History tables after the batch is posted, as it does in the Work table prior to posting, this could prevent use of the same Batch ID again. Some (like me) might say this is a good thing because it would provide a solid audit trail between the batch and its transactions.
Continued here:
GPTip42day – Why can’t I see the Batch ID in SmartList after I post a GL batch?