Text to go in the release notes:
Prior to this patch, the VOID action would reverse payments and set the original credit to '0'.
With this patch, we bring the void action in line with other actions that can take place on the accounts system. The original credit amount is kept for audit purposes, we add a VOID line to the accountlines and offset it against the original credit (so that the amount outstanding is zero) and we reverse all the original offsets the credit may have been made against and record these reversals.
This all helps in future audits and gives additional detail for Koha's other internal processes (Like automated refunds having to discount void payments - See bug 28421)