Deleting the existing contents of the field overwrites the clipboard. So if I first copy the new IP to the clipboard, then delete the old IP from the field, then paste, it will be pasting the old IP instead of the new.
Nothing in the JavaScript for that touches the clipboard. I paste addresses in there all the time. That particular behavior would either have to be something amiss on your side, or some really weird jQuery action in an edge case configuration. In any case, I'll still see about keeping it an input field while it's blank and unfocused.