opencart/opencart — pull request #1113 by kabatza (2014-01-01 01:59:25+00:00)
Title: check for customer negative store credit balance before confirm order 

A quick and effective fix to prevent customers using the multiple browser trick and double-spent store credit resulting in complete orders but negative store balance.

Modification simply checks the customer balance on callback (confirm or update) and if the store-credit is negative it sets the order to pending and adds a red notice in the order history.