@bolom after reviewing this further I don't believe this is the appropriate fix for everyone.  A few lines above this there is a conditional check to determine if the checkout is taking place from the cart page or payment step of the checkout process, and then setting order_total depending which checkout method it is.  This would change things to work the same way for both steps and not remove the no longer used conditional.

Is this error during checkout from the cart or through the checkout pages?  Does your fix work through both methods or should it just be effecting the order_total being set in the conditional block?  Could the error your having be related to #107 and could you try testing the fix used there?