Iirc, a browser or os does not send the file to any application in the order they are selected but rather any order the file picker chooses. So the real solution is to have a separate step to review/edit the upload before posting.
Edit : I mean it will be a new feature and not a bug
Yeah, that is correct. Firefox and chrome will return the order of the file picker. So unless you already sorted it in the file picker, the ui must somehow add an extra step before uploading as you cannot get the data of their selection order.
If that was your case, then it is absolutely a bug that can be fixed on the client side without adding new features.