It looks like your test source has not reached us for some reason.
However, do you actually call GetUploadStream with the same path both times? This method actually truncates the file, which means that the result of your code above would be a file with 1048576 zeros followed by some data. If this is the case, please call GetStream(path, FileMode.OpenOrCreate, FileAccess.Write) instead of GetUploadStream(path). We'll clarify this in the documentation - sorry for the confusion!