@@Mort-lemur   Question 1: I was wondering when you add a new order_total field (ot_custom) does it calculate the taxes correctly?   Question 2: And can you add a new ot_custom field in AJAX mode? I couldn't. Because when I enter the title I have to click "tab-key" or click with my mouse cursor on the amount field but just at that moment the page updates (AJAX) and it disappears.   If your answer for question 1 is "no" then look at this following fix. (from bugfunder, 23. Jan. 2011, http