Thanks for bringing this to our attention. We noticed that the voucher number before posting gets changed to a different series after posting. This voucher series is mapped to the AP invoice journal name and the AP Parameters → Number sequences → Invoice voucher for a sales tax book. 

If a credit note (an invoice where the vendor side is debited) is created, then the next invoice transaction skips the number sequence to one number ahead.

The voucher sequence is not working consistently when creating credit notes. The next sequence always gets skipped whenever a credit note is created. However, when a manual invoice is created, the sequence works correctly. The main intention of this idea is to correct the voucher sequence which is not working consistently when creating credit notes. The next sequence always does not want to be skipped whenever a credit note is created.