On one article I noticed that when I change the quantity via the browser item editor the quantity field always shows exactly one more than the quantity available field. So when i enter '0', it will be '1'. If I enter '10' it will be '11'. Is that behaviour intended? I don'think I noticed it before on another item.

When calling ReviseFixedPriceItem I'm able to set the quantity field as well as quantity available. That seems a little odd. When creating an item in the browser the quantity will always be the number that has been initially entered. Subsequent changes only change the quantity available value. Is that correct? If so, why can the quantity field be modified via the API call?