Comment 2 for bug 1104139

It's the javascript on the client side doing this, so refund amounts should simply _show_ as negative, they don't have to _be_ negative. I would suggest to change account/account_invoice_view.xml so that the "invoice_tree" record doesn't use "amount_total" etc. but instead use something new like "amount_total_signed" which would be the same but where desired (e.g. refund) prepends a minus.

You could do this now by way of an add-on that provides the corresponding invoice functions and overrides the existing "invoice_tree" columns via xpath replace.

The current sum at the bottom is so useless, even hiding it would be an improvement.