Editing an order clears all totals

I have an issue where when an order is edited and totals updated, that a value previously added by "Multi Payment Fee" module to order_totals table gets deleted.

WaaBay (the module developer) said its by design for the store front and has at the moment no intention to make it work with the backend what I need, because if this is not working I can't use the order editing feature at all.

I am not sure to consider this to be a bug or not. The module works on the front end without problems.

EDIT:
I am not sure, but it looks like the problem must be somewhere in admin\view\template\sale\order_form.tpl

As a test do the Low Order Fee or Handling Fee modules work correctly? If so it likely to be a limitation of the module you are using.

The low order fee seems to be working. So you are probably right. Now its only the question how to fix this, coz the author has so far no intention to do it. Anyway, thanks for the response.

I found out the cause...
The multi_payment_fee module expects data located in $this->session->data, but in case of catalog\controller\checkout\manual.php this information is not available like in normal conditions.
So I have to improvize somehow, because MPFrequires the information which payment method is used to calculate the fee. (i.e. paypal or COD)