We've got the SP5 update and we still just had AP-B post all debits to a transaction. It does not do it every time just occasionally.

OK, we have identified the cause and are working on a fix.  Meanwhile, here is what is going on and how to avoid it:
 
If you get past the voucher number and have entered dates, voucher type, etc. and then realize the voucher number is wrong, if you use the mouse to click back to the voucher number and fix it and then use the mouse to click back to the amount or wherever you were, it will post with the error.  If you tab through all the fields again after fixing the voucher number then it will post properly.  We will get it fixed but meanwhile, tab through all the fields after making a correction rather than using the mouse.