You're in luck, this was a quick fix (I hope). Open
admin/includes/super_edit.php and find this block of text:
Code:
elseif($ot_class == "ot_gv" || $ot_class == "ot_coupon" || $ot_class == "ot_group_pricing") {
$running_total -= $ot_value;
}
Create a new line directly after it (i.e. after the ending curly brace "}"), and add the following new block of code:
Code:
elseif ($ot_value < 0) {
$ot_value = abs($ot_value);
$ot_class = "ot_coupon";
$running_total -= $ot_value;
}
Upload the file to your server and try another negative number. Remember that you can delete an order total entry by completely deleting the text and value from the order screen.