The <item> link is lost once a user sends it to a channel. If you make a mistake and send it to the wrong channel, you can't just press up, correct your mistake, and press enter to send it again. If you do this <link> just inserts nothing. To correct a mistake, you must do all this, then first reselect the item you want to link, select "Link" again, and THEN press enter.
There's no reason to unset <item>. So don't.