>> The item is being selected so that is fixed but the net, vat and gross fields have become spin controls. This was not the case in 6.15 I am sure.
>> I checked and the fields were type Number.
Type"Number" is rendered differently in different browsers. Some make them spin boxes, some don't. This is, alas, not new, so I think the difference you are seeing there is just in the browser you are using.
you can indeed change to String to force the spin boxes off.
Regarding the Item lookup thing, I changed the fields to be Strings here, but it seems to be working the same - ie Nett is set. Did you change anything other than the type of the field? Perhaps experimenting with the Spin buttons?