Updating field on order page not working

Hi there,

On my checkout page there is a field created with checkout manager for the client to insert a company tax code.

Today, client placed an order and, soon after, called saying that he forgot to insert this tax code.

So I went to the order page, I click on the little pencil, insert manually the code, and click on Update.

Problem is, the field is not updated, no mattar what I do, it does not save.

Any clue?