Ok did some googling and found this pic of a UC rack (which I assume has the same shaft as an LH/LX rack). I can now see the stepped down end you're talking about. So just to clarify, that stepped down end has no flat recess in it for the cotter pin? The flat recess is on the large part of the shaft. Therefore making it impossible to fit correctly without cutting off the stepped down section? I don't remember seeing this on mine, but I'm still keen to check it out.
Not to be picky but I don't think that's a UC rack. UC's don't have rubber mounting bushes, they have aluminium bushes.